Commit graph

86 commits

Author SHA1 Message Date
Jinke Han
14a6e2eb7d block: don't allow the same type rq_qos add more than once
In our test of iocost, we encountered some list add/del corruptions of
inner_walk list in ioc_timer_fn.

The reason can be described as follows:

cpu 0					cpu 1
ioc_qos_write				ioc_qos_write

ioc = q_to_ioc(queue);
if (!ioc) {
        ioc = kzalloc();
					ioc = q_to_ioc(queue);
					if (!ioc) {
						ioc = kzalloc();
						...
						rq_qos_add(q, rqos);
					}
        ...
        rq_qos_add(q, rqos);
        ...
}

When the io.cost.qos file is written by two cpus concurrently, rq_qos may
be added to one disk twice. In that case, there will be two iocs enabled
and running on one disk. They own different iocgs on their active list. In
the ioc_timer_fn function, because of the iocgs from two iocs have the
same root iocg, the root iocg's walk_list may be overwritten by each other
and this leads to list add/del corruptions in building or destroying the
inner_walk list.

And so far, the blk-rq-qos framework works in case that one instance for
one type rq_qos per queue by default. This patch make this explicit and
also fix the crash above.

Signed-off-by: Jinke Han <hanjinke.666@bytedance.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20220720093616.70584-1-hanjinke.666@bytedance.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2022-07-20 06:44:14 -06:00
Bart Van Assche
62c159a03d blk-iocost: Simplify ioc_rqos_done()
Leave out the superfluous "& REQ_OP_MASK" code. The definition of req_op()
shows that that code is superfluous:

 #define req_op(req) ((req)->cmd_flags & REQ_OP_MASK)

Compile-tested only.

Cc: Tejun Heo <tj@kernel.org>
Acked-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20220615225549.1054905-2-bvanassche@acm.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2022-06-27 06:29:11 -06:00
Linus Torvalds
115cd47132 for-5.19/block-2022-05-22
-----BEGIN PGP SIGNATURE-----
 
 iQJEBAABCAAuFiEEwPw5LcreJtl1+l5K99NY+ylx4KYFAmKKrUsQHGF4Ym9lQGtl
 cm5lbC5kawAKCRD301j7KXHgpgDjD/44hY9h0JsOLoRH1IvFtuaH6n718JXuqG17
 hHCfmnAUVqj2jT00IUbVlUTd905bCGpfrodBL3PAmPev1zZHOUd/MnJKrSynJ+/s
 NJEMZQaHxLmocNDpJ1sZo7UbAFErsZXB0gVYUO8cH2bFYNu84H1mhRCOReYyqmvQ
 aIAASX5qRB/ciBQCivzAJl2jTdn4WOn5hWi9RLidQB7kSbaXGPmgKAuN88WI4H7A
 zQgAkEl2EEquyMI5tV1uquS7engJaC/4PsenF0S9iTyrhJLjneczJBJZKMLeMR8d
 sOm6sKJdpkrfYDyaA4PIkgmLoEGTtwGpqGHl4iXTyinUAxJoca5tmPvBb3wp66GE
 2Mr7pumxc1yJID2VHbsERXlOAX3aZNCowx2gum2MTRIO8g11Eu3aaVn2kv37MBJ2
 4R2a/cJFl5zj9M8536cG+Yqpy0DDVCCQKUIqEupgEu1dyfpznyWH5BTAHXi1E8td
 nxUin7uXdD0AJkaR0m04McjS/Bcmc1dc6I8xvkdUFYBqYCZWpKOTiEpIBlHg0XJA
 sxdngyz5lSYTGVA4o4QCrdR0Tx1n36A1IYFuQj0wzxBJYZ02jEZuII/A3dd+8hiv
 EY+VeUQeVIXFFuOcY+e0ScPpn7Nr17hAd1en/j2Hcoe4ZE8plqG2QTcnwgflcbis
 iomvJ4yk0Q==
 =0Rw1
 -----END PGP SIGNATURE-----

Merge tag 'for-5.19/block-2022-05-22' of git://git.kernel.dk/linux-block

Pull block updates from Jens Axboe:
 "Here are the core block changes for 5.19. This contains:

   - blk-throttle accounting fix (Laibin)

   - Series removing redundant assignments (Michal)

   - Expose bio cache via the bio_set, so that DM can use it (Mike)

   - Finish off the bio allocation interface cleanups by dealing with
     the weirdest member of the family. bio_kmalloc combines a kmalloc
     for the bio and bio_vecs with a hidden bio_init call and magic
     cleanup semantics (Christoph)

   - Clean up the block layer API so that APIs consumed by file systems
     are (almost) only struct block_device based, so that file systems
     don't have to poke into block layer internals like the
     request_queue (Christoph)

   - Clean up the blk_execute_rq* API (Christoph)

   - Clean up various lose end in the blk-cgroup code to make it easier
     to follow in preparation of reworking the blkcg assignment for bios
     (Christoph)

   - Fix use-after-free issues in BFQ when processes with merged queues
     get moved to different cgroups (Jan)

   - BFQ fixes (Jan)

   - Various fixes and cleanups (Bart, Chengming, Fanjun, Julia, Ming,
     Wolfgang, me)"

* tag 'for-5.19/block-2022-05-22' of git://git.kernel.dk/linux-block: (83 commits)
  blk-mq: fix typo in comment
  bfq: Remove bfq_requeue_request_body()
  bfq: Remove superfluous conversion from RQ_BIC()
  bfq: Allow current waker to defend against a tentative one
  bfq: Relax waker detection for shared queues
  blk-cgroup: delete rcu_read_lock_held() WARN_ON_ONCE()
  blk-throttle: Set BIO_THROTTLED when bio has been throttled
  blk-cgroup: Remove unnecessary rcu_read_lock/unlock()
  blk-cgroup: always terminate io.stat lines
  block, bfq: make bfq_has_work() more accurate
  block, bfq: protect 'bfqd->queued' by 'bfqd->lock'
  block: cleanup the VM accounting in submit_bio
  block: Fix the bio.bi_opf comment
  block: reorder the REQ_ flags
  blk-iocost: combine local_stat and desc_stat to stat
  block: improve the error message from bio_check_eod
  block: allow passing a NULL bdev to bio_alloc_clone/bio_init_clone
  block: remove superfluous calls to blkcg_bio_issue_init
  kthread: unexport kthread_blkcg
  blk-cgroup: cleanup blkcg_maybe_throttle_current
  ...
2022-05-23 13:56:39 -07:00
Wolfgang Bumiller
3607849df4 blk-cgroup: always terminate io.stat lines
With the removal of seq_get_buf in blkcg_print_one_stat, we
cannot make adding the newline conditional on there being
relevant stats because the name was already written out
unconditionally.
Otherwise we may end up with multiple device names in one
line which is confusing and doesn't follow the nested-keyed
file format.

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
Fixes: 252c651a4c ("blk-cgroup: stop using seq_get_buf")
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20220111083159.42340-1-w.bumiller@proxmox.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2022-05-17 06:11:17 -06:00
Chengming Zhou
2a371f7d5f blk-iocost: combine local_stat and desc_stat to stat
When we flush usage, wait, indebt stat in iocg_flush_stat(), we use
local_stat and desc_stat, which has no point since the leaf iocg
only has local_stat and the inner iocg only has desc_stat. Also
we don't need to flush percpu abs_vusage for these inner iocgs.

This patch combine local_stat and desc_stat to stat, only flush
percpu abs_vusage for active leaf iocgs, then build inner walk
list to propagate.

Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20220510034757.21761-1-zhouchengming@bytedance.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2022-05-11 17:05:52 -06:00
Tejun Heo
8c936f9ea1 iocost: don't reset the inuse weight of under-weighted debtors
When an iocg is in debt, its inuse weight is owned by debt handling and
should stay at 1. This invariant was broken when determining the amount of
surpluses at the beginning of donation calculation - when an iocg's
hierarchical weight is too low, the iocg is excluded from donation
calculation and its inuse is reset to its active regardless of its
indebtedness, triggering warnings like the following:

 WARNING: CPU: 5 PID: 0 at block/blk-iocost.c:1416 iocg_kick_waitq+0x392/0x3a0
 ...
 RIP: 0010:iocg_kick_waitq+0x392/0x3a0
 Code: 00 00 be ff ff ff ff 48 89 4d a8 e8 98 b2 70 00 48 8b 4d a8 85 c0 0f 85 4a fe ff ff 0f 0b e9 43 fe ff ff 0f 0b e9 4d fe ff ff <0f> 0b e9 50 fe ff ff e8 a2 ae 70 00 66 90 0f 1f 44 00 00 55 48 89
 RSP: 0018:ffffc90000200d08 EFLAGS: 00010016
 ...
  <IRQ>
  ioc_timer_fn+0x2e0/0x1470
  call_timer_fn+0xa1/0x2c0
 ...

As this happens only when an iocg's hierarchical weight is negligible, its
impact likely is limited to triggering the warnings. Fix it by skipping
resetting inuse of under-weighted debtors.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Rik van Riel <riel@surriel.com>
Fixes: c421a3eb2e ("blk-iocost: revamp debt handling")
Cc: stable@vger.kernel.org # v5.10+
Link: https://lore.kernel.org/r/YmjODd4aif9BzFuO@slm.duckdns.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2022-04-27 08:41:11 -06:00
Ming Lei
672fdcf0e7 block: partition include/linux/blk-cgroup.h
Partition include/linux/blk-cgroup.h into two parts: one is public part,
the other is block layer private part.

Suggested by Christoph Hellwig.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220211101149.2368042-4-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2022-02-11 10:02:41 -07:00
Tejun Heo
edaa26334c iocost: Fix divide-by-zero on donation from low hweight cgroup
The donation calculation logic assumes that the donor has non-zero
after-donation hweight, so the lowest active hweight a donating cgroup can
have is 2 so that it can donate 1 while keeping the other 1 for itself.
Earlier, we only donated from cgroups with sizable surpluses so this
condition was always true. However, with the precise donation algorithm
implemented, f1de2439ec ("blk-iocost: revamp donation amount
determination") made the donation amount calculation exact enabling even low
hweight cgroups to donate.

This means that in rare occasions, a cgroup with active hweight of 1 can
enter donation calculation triggering the following warning and then a
divide-by-zero oops.

 WARNING: CPU: 4 PID: 0 at block/blk-iocost.c:1928 transfer_surpluses.cold+0x0/0x53 [884/94867]
 ...
 RIP: 0010:transfer_surpluses.cold+0x0/0x53
 Code: 92 ff 48 c7 c7 28 d1 ab b5 65 48 8b 34 25 00 ae 01 00 48 81 c6 90 06 00 00 e8 8b 3f fe ff 48 c7 c0 ea ff ff ff e9 95 ff 92 ff <0f> 0b 48 c7 c7 30 da ab b5 e8 71 3f fe ff 4c 89 e8 4d 85 ed 74 0
4
 ...
 Call Trace:
  <IRQ>
  ioc_timer_fn+0x1043/0x1390
  call_timer_fn+0xa1/0x2c0
  __run_timers.part.0+0x1ec/0x2e0
  run_timer_softirq+0x35/0x70
 ...
 iocg: invalid donation weights in /a/b: active=1 donating=1 after=0

Fix it by excluding cgroups w/ active hweight < 2 from donating. Excluding
these extreme low hweight donations shouldn't affect work conservation in
any meaningful way.

Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: f1de2439ec ("blk-iocost: revamp donation amount determination")
Cc: stable@vger.kernel.org # v5.10+
Link: https://lore.kernel.org/r/Ybfh86iSvpWKxhVM@slm.duckdns.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2021-12-14 06:58:15 -07:00
Pavel Begunkov
ed6cddefdf block: convert the rest of block to bdev_get_queue
Convert bdev->bd_disk->queue to bdev_get_queue(), it's uses a cached
queue pointer and so is faster.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/addf6ea988c04213697ba3684c853e4ed7642a39.1634219547.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2021-10-18 06:17:37 -06:00
Linus Torvalds
679369114e for-5.15/block-2021-08-30
-----BEGIN PGP SIGNATURE-----
 
 iQJEBAABCAAuFiEEwPw5LcreJtl1+l5K99NY+ylx4KYFAmEs6H0QHGF4Ym9lQGtl
 cm5lbC5kawAKCRD301j7KXHgpukbD/9Qk9fQte+WJVmpbdvhV40gcKBVnGOVH0ke
 k+36x6AB/gWKnFHwtprsSyVqPxmzqwTv9VIq5l/s3Vydt3L61znvTneBeN03Wlkn
 UTxD0lY8HzyVWnZb82LBBjjy7cs6EzrFG4kBH/ZiTAyTcBsCAvzo5J7mywb4gFjj
 L/HeBq58EJ3WCUlxlVW1ijctvi7wnGoaH5bZY1TE00GGT6TysN2bEPfzjkuYHrDz
 RqhoQdWPLDz6h3x9lAncPw2MWlcmlGvJ96ABseAKFPKvXxE2PzgolSoQfVUUJtko
 bqGyy2ns+pxN11SrcGYjogEKVKhONoms/5UN1RtwRBVsgvecxlHER/SgyZ8luBDo
 lFhVXulkSjpswbWutRy3USge98GwMu2Z4ppP2CDmO7hkQd0DF8sL0kPKyaREkcHi
 NmsD/0zF2uUhUVN+PRC/MuzngAmL4Mmxjk70L+MohlK7e+H3pnEo1ec3OMcXe+wB
 dG6t/BFD9bYmj0UjsHeXEoR/iRuvSba1L8zBz5dhRaHH6DvdycYhpynXWWlU3C8K
 3nzEVVpcDINMsiRl1Vqb6g6HsMwHIH84FRl7Mc51UmhW9C4gLfWMCt1guQuzOj72
 yEbmCLydE/FR2IUPY7eqX8hRG8GTUlMtSvGdgnvBOcWj+K3buT/c5yVTHgTrN8ox
 LCOXHSvV6w==
 =S8fs
 -----END PGP SIGNATURE-----

Merge tag 'for-5.15/block-2021-08-30' of git://git.kernel.dk/linux-block

Pull block updates from Jens Axboe:
 "Nothing major in here - lots of good cleanups and tech debt handling,
  which is also evident in the diffstats. In particular:

   - Add disk sequence numbers (Matteo)

   - Discard merge fix (Ming)

   - Relax disk zoned reporting restrictions (Niklas)

   - Bio error handling zoned leak fix (Pavel)

   - Start of proper add_disk() error handling (Luis, Christoph)

   - blk crypto fix (Eric)

   - Non-standard GPT location support (Dmitry)

   - IO priority improvements and cleanups (Damien)o

   - blk-throtl improvements (Chunguang)

   - diskstats_show() stack reduction (Abd-Alrhman)

   - Loop scheduler selection (Bart)

   - Switch block layer to use kmap_local_page() (Christoph)

   - Remove obsolete disk_name helper (Christoph)

   - block_device refcounting improvements (Christoph)

   - Ensure gendisk always has a request queue reference (Christoph)

   - Misc fixes/cleanups (Shaokun, Oliver, Guoqing)"

* tag 'for-5.15/block-2021-08-30' of git://git.kernel.dk/linux-block: (129 commits)
  sg: pass the device name to blk_trace_setup
  block, bfq: cleanup the repeated declaration
  blk-crypto: fix check for too-large dun_bytes
  blk-zoned: allow BLKREPORTZONE without CAP_SYS_ADMIN
  blk-zoned: allow zone management send operations without CAP_SYS_ADMIN
  block: mark blkdev_fsync static
  block: refine the disk_live check in del_gendisk
  mmc: sdhci-tegra: Enable MMC_CAP2_ALT_GPT_TEGRA
  mmc: block: Support alternative_gpt_sector() operation
  partitions/efi: Support non-standard GPT location
  block: Add alternative_gpt_sector() operation
  bio: fix page leak bio_add_hw_page failure
  block: remove CONFIG_DEBUG_BLOCK_EXT_DEVT
  block: remove a pointless call to MINOR() in device_add_disk
  null_blk: add error handling support for add_disk()
  virtio_blk: add error handling support for add_disk()
  block: add error handling for device_add_disk / add_disk
  block: return errors from disk_alloc_events
  block: return errors from blk_integrity_add
  block: call blk_register_queue earlier in device_add_disk
  ...
2021-08-30 18:52:11 -07:00
Christoph Hellwig
252c651a4c blk-cgroup: stop using seq_get_buf
seq_get_buf is a crutch that undoes all the memory safety of the
seq_file interface.  Use the normal seq_printf interfaces instead.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20210810152623.1796144-2-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2021-08-16 10:53:01 -06:00
Ming Lei
11431e26c9 blk-iocost: fix lockdep warning on blkcg->lock
blkcg->lock depends on q->queue_lock which may depend on another driver
lock required in irq context, one example is dm-thin:

	Chain exists of:
	  &pool->lock#3 --> &q->queue_lock --> &blkcg->lock

	 Possible interrupt unsafe locking scenario:

	       CPU0                    CPU1
	       ----                    ----
	  lock(&blkcg->lock);
	                               local_irq_disable();
	                               lock(&pool->lock#3);
	                               lock(&q->queue_lock);
	  <Interrupt>
	    lock(&pool->lock#3);

Fix the issue by using spin_lock_irq(&blkcg->lock) in ioc_weight_write().

Cc: Tejun Heo <tj@kernel.org>
Reported-by: Bruno Goncalves <bgoncalv@redhat.com>
Link: https://lore.kernel.org/linux-block/CA+QYu4rzz6079ighEanS3Qq_Dmnczcf45ZoJoHKVLVATTo1e4Q@mail.gmail.com/T/#u
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20210803070608.1766400-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2021-08-09 20:00:26 -06:00
Tejun Heo
5ab189cf3a blk-iocost: fix operation ordering in iocg_wake_fn()
iocg_wake_fn() open-codes wait_queue_entry removal and wakeup because it
wants the wq_entry to be always removed whether it ended up waking the
task or not. finish_wait() tests whether wq_entry needs removal without
grabbing the wait_queue lock and expects the waker to use
list_del_init_careful() after all waking operations are complete, which
iocg_wake_fn() didn't do. The operation order was wrong and the regular
list_del_init() was used.

The result is that if a waiter wakes up racing the waker, it can free pop
the wq_entry off stack before the waker is still looking at it, which can
lead to a backtrace like the following.

  [7312084.588951] general protection fault, probably for non-canonical address 0x586bf4005b2b88: 0000 [#1] SMP
  ...
  [7312084.647079] RIP: 0010:queued_spin_lock_slowpath+0x171/0x1b0
  ...
  [7312084.858314] Call Trace:
  [7312084.863548]  _raw_spin_lock_irqsave+0x22/0x30
  [7312084.872605]  try_to_wake_up+0x4c/0x4f0
  [7312084.880444]  iocg_wake_fn+0x71/0x80
  [7312084.887763]  __wake_up_common+0x71/0x140
  [7312084.895951]  iocg_kick_waitq+0xe8/0x2b0
  [7312084.903964]  ioc_rqos_throttle+0x275/0x650
  [7312084.922423]  __rq_qos_throttle+0x20/0x30
  [7312084.930608]  blk_mq_make_request+0x120/0x650
  [7312084.939490]  generic_make_request+0xca/0x310
  [7312084.957600]  submit_bio+0x173/0x200
  [7312084.981806]  swap_readpage+0x15c/0x240
  [7312084.989646]  read_swap_cache_async+0x58/0x60
  [7312084.998527]  swap_cluster_readahead+0x201/0x320
  [7312085.023432]  swapin_readahead+0x2df/0x450
  [7312085.040672]  do_swap_page+0x52f/0x820
  [7312085.058259]  handle_mm_fault+0xa16/0x1420
  [7312085.066620]  do_page_fault+0x2c6/0x5c0
  [7312085.074459]  page_fault+0x2f/0x40

Fix it by switching to list_del_init_careful() and putting it at the end.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Rik van Riel <riel@surriel.com>
Fixes: 7caa47151a ("blkcg: implement blk-iocost")
Cc: stable@vger.kernel.org # v5.4+
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2021-07-27 19:25:37 -06:00
Tejun Heo
e9f4eee9a0 blk-iocost: fix weight updates of inner active iocgs
When the weight of an active iocg is updated, weight_updated() is called
which in turn calls __propagate_weights() to update the active and inuse
weights so that the effective hierarchical weights are update accordingly.

The current implementation is incorrect for inner active nodes. For an
active leaf iocg, inuse can be any value between 1 and active and the
difference represents how much the iocg is donating. When weight is updated,
as long as inuse is clamped between 1 and the new weight, we're alright and
this is what __propagate_weights() currently implements.

However, that's not how an active inner node's inuse is set. An inner node's
inuse is solely determined by the ratio between the sums of inuse's and
active's of its children - ie. they're results of propagating the leaves'
active and inuse weights upwards. __propagate_weights() incorrectly applies
the same clamping as for a leaf when an active inner node's weight is
updated. Consider a hierarchy which looks like the following with saturating
workloads in AA and BB.

     R
   /   \
  A     B
  |     |
 AA     BB

1. For both A and B, active=100, inuse=100, hwa=0.5, hwi=0.5.

2. echo 200 > A/io.weight

3. __propagate_weights() update A's active to 200 and leave inuse at 100 as
   it's already between 1 and the new active, making A:active=200,
   A:inuse=100. As R's active_sum is updated along with A's active,
   A:hwa=2/3, B:hwa=1/3. However, because the inuses didn't change, the
   hwi's remain unchanged at 0.5.

4. The weight of A is now twice that of B but AA and BB still have the same
   hwi of 0.5 and thus are doing the same amount of IOs.

Fix it by making __propgate_weights() always calculate the inuse of an
active inner iocg based on the ratio of child_inuse_sum to child_active_sum.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Dan Schatzberg <dschatzberg@fb.com>
Fixes: 7caa47151a ("blkcg: implement blk-iocost")
Cc: stable@vger.kernel.org # v5.4+
Link: https://lore.kernel.org/r/YJsxnLZV1MnBcqjj@slm.duckdns.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2021-05-11 20:50:35 -06:00
Tejun Heo
f46ec84b5a blk-iocost: don't ignore vrate_min on QD contention
ioc_adjust_base_vrate() ignored vrate_min when rq_wait_pct indicates that
there is QD contention. The reasoning was that QD depletion always reliably
indicates device saturation and thus it's safe to override user specified
vrate_min. However, this sometimes leads to unnecessary throttling,
especially on really fast devices, because vrate adjustments have delays and
inertia. It also confuses users because the behavior violates the explicitly
specified configuration.

This patch drops the special case handling so that vrate_min is always
applied.

Signed-off-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/YIIo1HuyNmhDeiNx@slm.duckdns.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2021-04-26 06:44:18 -06:00
Tejun Heo
d16baa3f14 blk-iocost: fix NULL iocg deref from racing against initialization
When initializing iocost for a queue, its rqos should be registered before
the blkcg policy is activated to allow policy data initiailization to lookup
the associated ioc. This unfortunately means that the rqos methods can be
called on bios before iocgs are attached to all existing blkgs.

While the race is theoretically possible on ioc_rqos_throttle(), it mostly
happened in ioc_rqos_merge() due to the difference in how they lookup ioc.
The former determines it from the passed in @rqos and then bails before
dereferencing iocg if the looked up ioc is disabled, which most likely is
the case if initialization is still in progress. The latter looked up ioc by
dereferencing the possibly NULL iocg making it a lot more prone to actually
triggering the bug.

* Make ioc_rqos_merge() use the same method as ioc_rqos_throttle() to look
  up ioc for consistency.

* Make ioc_rqos_throttle() and ioc_rqos_merge() test for NULL iocg before
  dereferencing it.

* Explain the danger of NULL iocgs in blk_iocost_init().

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Jonathan Lemon <bsd@fb.com>
Cc: stable@vger.kernel.org # v5.4+
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2021-01-05 11:33:32 -07:00
Baolin Wang
76efc1c770 blk-iocost: Add iocg idle state tracepoint
It will be helpful to trace the iocg's whole state, including active and
idle state. And we can easily expand the original iocost_iocg_activate
trace event to support a state trace class, including active and idle
state tracing.

Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-12-17 07:55:44 -07:00
Baolin Wang
926f75f6a9 blk-iocost: Factor out the base vrate change into a separate function
Factor out the base vrate change code into a separate function
to fimplify the ioc_timer_fn().

No functional change.

Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-12-07 13:20:31 -07:00
Baolin Wang
2474787a75 blk-iocost: Factor out the active iocgs' state check into a separate function
Factor out the iocgs' state check into a separate function to
simplify the ioc_timer_fn().

No functional change.

Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-12-07 13:20:31 -07:00
Baolin Wang
c09245f61c blk-iocost: Move the usage ratio calculation to the correct place
We only use the hweight based usage ratio to calculate the new
hweight_inuse of the iocg to decide if this iocg can donate some
surplus vtime.

Thus move the usage ratio calculation to the correct place to
avoid unnecessary calculation for some vtime shortage iocgs.

Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-12-07 13:20:31 -07:00
Baolin Wang
647c9f03b2 blk-iocost: Remove unnecessary advance declaration
Remove unnecessary advance declaration of struct ioc_gq.

Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-12-07 13:20:31 -07:00
Baolin Wang
5ba1add216 blk-iocost: Fix some typos in comments
Fix some typos in comments.

Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-12-07 13:20:31 -07:00
Christoph Hellwig
22ae8ce8b8 block: simplify bdev/disk lookup in blkdev_get
To simplify block device lookup and a few other upcoming areas, make sure
that we always have a struct block_device available for each disk and
each partition, and only find existing block devices in bdget.  The only
downside of this is that each device and partition uses a little more
memory.  The upside will be that a lot of code can be simplified.

With that all we need to look up the block device is to lookup the inode
and do a few sanity checks on the gendisk, instead of the separate lookup
for the gendisk.  For blk-cgroup which wants to access a gendisk without
opening it, a new blkdev_{get,put}_no_open low-level interface is added
to replace the previous get_gendisk use.

Note that the change to look up block device directly instead of the two
step lookup using struct gendisk causes a subtile change in behavior:
accessing a non-existing partition on an existing block device can now
cause a call to request_module.  That call is harmless, and in practice
no recent system will access these nodes as they aren't created by udev
and static /dev/ setups are unusual.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-12-01 14:53:39 -07:00
Yufen Yu
75e6c00fc7 block: use helper function to test queue register
We have defined common interface blk_queue_registered() to
test QUEUE_FLAG_REGISTERED. Just use it.

Signed-off-by: Yufen Yu <yuyufen@huawei.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-10-09 12:34:06 -06:00
Baolin Wang
fa1c3eaf4d block: Remove redundant 'return' statement
Remove redundant 'return' statement for 'void' functions.

Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-10-08 07:59:48 -06:00
Tejun Heo
bec02dbbaf iocost: consider iocgs with active delays for debt forgiveness
An iocg may have 0 debt but non-zero delay. The current debt forgiveness
logic doesn't act on such iocgs. This can lead to unexpected behaviors - an
iocg with a little bit of debt will have its delay canceled through debt
forgiveness but one w/o any debt but active delay will have to wait out
until its delay decays out.

This patch updates the debt handling logic so that it treats delays the same
as debts. If either debt or delay is active, debt forgiveness logic kicks in
and acts on both the same way.

Also, avoid turning the debt and delay directly to zero as that can confuse
state transitions.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-25 08:35:02 -06:00
Tejun Heo
c5a6561b8d iocost: add iocg_forgive_debt tracepoint
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-25 08:35:02 -06:00
Tejun Heo
c7af2a003a iocost: reimplement debt forgiveness using average usage
Debt forgiveness logic was counting the number of consecutive !busy periods
as the trigger condition. While this usually works, it can easily be thrown
off by temporary fluctuations especially on configurations w/ short periods.

This patch reimplements debt forgiveness so that:

* Use the average usage over the forgiveness period instead of counting
  consecutive periods.

* Debt is reduced at around the target rate (1/2 every 100ms) regardless of
  ioc period duration.

* Usage threshold is raised to 50%. Combined with the preceding changes and
  the switch to average usage, this makes debt forgivness a lot more
  effective at reducing the amount of unnecessary idleness.

* Constants are renamed with DFGV_ prefix.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-25 08:35:02 -06:00
Tejun Heo
d95178410b iocost: recalculate delay after debt reduction
Debt sets the initial delay duration which is decayed over time. The current
debt reduction halved the debt but didn't change the delay. It prevented
future debts from increasing delay but didn't do anything to lower the
existing delay, limiting the mechanism's ability to reduce unnecessary
idling.

Reset iocg->delay to 0 after debt reduction so that iocg_kick_waitq()
recalculates new delay value based on the reduced debt amount.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-25 08:35:02 -06:00
Tejun Heo
33a1fe6d82 iocost: replace nr_shortages cond in ioc_forgive_debts() with busy_level one
Debt reduction was blocked if any iocg was short on budget in the past
period to avoid reducing debts while some iocgs are saturated. However, this
ends up unnecessarily blocking debt reduction due to temporary local
imbalances when the device is generally being underutilized, while also
failing to block when the underlying device is overwhelmed and the usage
becomes low from high latency.

Given that debt accumulation mostly happens with swapout bursts which can
significantly deteriorate the underlying device's latency response, the
current logic is not great.

Let's replace it with ioc->busy_level based condition so that we block debt
reduction when the underlying device is being saturated. ioc_forgive_debts()
call is moved after busy_level determination.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-25 08:35:02 -06:00
Tejun Heo
ab8df828b5 iocost: factor out ioc_forgive_debts()
Debt reduction logic is going to be improved and expanded. Factor it out
into ioc_forgive_debts() and generalize the comment a bit. No functional
change.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-25 08:35:02 -06:00
Tejun Heo
aa67db24b6 iocost: fix infinite loop bug in adjust_inuse_and_calc_cost()
adjust_inuse_and_calc_cost() is responsible for reducing the amount of
donated weights dynamically in period as the budget runs low. Because we
don't want to do full donation calculation in period, we keep latching up
inuse by INUSE_ADJ_STEP_PCT of the active weight of the cgroup until the
resulting hweight_inuse is satisfactory.

Unfortunately, the adj_step calculation was reading the active weight before
acquiring ioc->lock. Because the current thread could have lost race to
activate the iocg to another thread before entering this function, it may
read the active weight as zero before acquiring ioc->lock. When this
happens, the adj_step is calculated as zero and the incremental adjustment
loop becomes an infinite one.

Fix it by fetching the active weight after acquiring ioc->lock.

Fixes: b0853ab4a2 ("blk-iocost: revamp in-period donation snapbacks")
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-14 17:25:39 -06:00
Tejun Heo
769b628de0 blk-iocost: fix divide-by-zero in transfer_surpluses()
Conceptually, root_iocg->hweight_donating must be less than WEIGHT_ONE but
all hweight calculations round up and thus it may end up >= WEIGHT_ONE
triggering divide-by-zero and other issues. Bound the value to avoid
surprises.

Fixes: e08d02aa5f ("blk-iocost: implement Andy's method for donation weight updates")
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-11 16:41:47 -06:00
Tejun Heo
f0bf84a5df blk-iocost: add three debug stat - cost.wait, indebt and indelay
These are really cheap to collect and can be useful in debugging iocost
behavior. Add them as debug stats for now.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-01 19:38:33 -06:00
Tejun Heo
0460375517 blk-iocost: restore inuse update tracepoints
Update and restore the inuse update tracepoints.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-01 19:38:33 -06:00
Tejun Heo
ac33e91e2d blk-iocost: implement vtime loss compensation
When an iocg accumulates too much vtime or gets deactivated, we throw away
some vtime, which lowers the overall device utilization. As the exact amount
which is being thrown away is known, we can compensate by accelerating the
vrate accordingly so that the extra vtime generated in the current period
matches what got lost.

This significantly improves work conservation when involving high weight
cgroups with intermittent and bursty IO patterns.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-01 19:38:33 -06:00
Tejun Heo
dda1315f18 blk-iocost: halve debts if device stays idle
A low weight iocg can amass a large amount of debt, for example, when
anonymous memory gets reclaimed aggressively. If the system has a lot of
memory paired with a slow IO device, the debt can span multiple seconds or
more. If there are no other subsequent IO issuers, the in-debt iocg may end
up blocked paying its debt while the IO device is idle.

This patch implements a mechanism to protect against such pathological
cases. If the device has been sufficiently idle for a substantial amount of
time, the debts are halved. The criteria are on the conservative side as we
want to resolve the rare extreme cases without impacting regular operation
by forgiving debts too readily.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-01 19:38:33 -06:00
Tejun Heo
5160a5a53c blk-iocost: implement delay adjustment hysteresis
Curently, iocost syncs the delay duration to the outstanding debt amount,
which seemed enough to protect the system from anon memory hogs. However,
that was mostly because the delay calcuation was using hweight_inuse which
quickly converges towards zero under debt for delay duration calculation,
often pusnishing debtors overly harshly for longer than deserved.

The previous patch fixed the delay calcuation and now the protection against
anonymous memory hogs isn't enough because the effect of delay is indirect
and non-linear and a huge amount of future debt can accumulate abruptly
while unthrottled.

This patch implements delay hysteresis so that delay is decayed
exponentially over time instead of getting cleared immediately as debt is
paid off. While the overall behavior is similar to the blk-cgroup
implementation used by blk-iolatency, a lot of the details are different and
due to the empirical nature of the mechanism, it's challenging to adapt the
mechanism for one controller without negatively impacting the other.

As the delay is gradually decayed now, there's no point in running it from
its own hrtimer. Periodic updates are now performed from ioc_timer_fn() and
the dedicated hrtimer is removed.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-01 19:38:32 -06:00
Tejun Heo
c421a3eb2e blk-iocost: revamp debt handling
Debt handling had several issues.

* How much inuse a debtor carries wasn't clearly defined. inuse would be
  driven down over time from not issuing IOs but it'd be better to clamp it
  to minimum immediately once in debt.

* How much can be paid off was determined by hweight_inuse. As inuse was
  driven down, the payment amount would fall together regardless of the
  debtor's active weight. This means that the debtors were punished harshly.

* ioc_rqos_merge() wasn't calling blkcg_schedule_throttle() after
  iocg_kick_delay().

This patch revamps debt handling so that

* Debt handling owns inuse for iocgs in debt and keeps them at zero.

* Payment amount is determined by hweight_active. This is more deterministic
  and safer than hweight_inuse but still far from ideal in that it doesn't
  factor in possible donations from other iocgs for debt payments. This
  likely needs further improvements in the future.

* iocg_rqos_merge() now calls blkcg_schedule_throttle() as necessary.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Andy Newell <newella@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-01 19:38:32 -06:00
Tejun Heo
b0853ab4a2 blk-iocost: revamp in-period donation snapbacks
When the margin drops below the minimum on a donating iocg, donation is
immediately canceled in full. There are a couple shortcomings with the
current behavior.

* It's abrupt. A small temporary budget deficit can lead to a wide swing in
  weight allocation and a large surplus.

* It's open coded in the issue path but not implemented for the merge path.
  A series of merges at a low inuse can make the iocg incur debts and stall
  incorrectly.

This patch reimplements in-period donation snapbacks so that

* inuse adjustment and cost calculations are factored into
  adjust_inuse_and_calc_cost() which is called from both the issue and merge
  paths.

* Snapbacks are more gradual. It occurs in quarter steps.

* A snapback triggers if the margin goes below the low threshold and is
  lower than the budget at the time of the last adjustment.

* For the above, __propagate_weights() stores the margin in
  iocg->saved_margin. Move iocg->last_inuse storing together into
  __propagate_weights() for consistency.

* Full snapback is guaranteed when there are waiters.

* With precise donation and gradual snapbacks, inuse adjustments are now a
  lot more effective and the value of scaling inuse on weight changes isn't
  clear. Removed inuse scaling from weight_update().

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-01 19:38:32 -06:00
Tejun Heo
f1de2439ec blk-iocost: revamp donation amount determination
iocost has various safety nets to combat inuse adjustment calculation
inaccuracies. With Andy's method implemented in transfer_surpluses(), inuse
adjustment calculations are now accurate and we can make donation amount
determinations accurate too.

* Stop keeping track of past usage history and using the maximum. Act on the
  immediate usage information.

* Remove donation constraints defined by SURPLUS_* constants. Donate
  whatever isn't used.

* Determine the donation amount so that the iocg will end up with
  MARGIN_TARGET_PCT budget at the end of the coming period assuming the same
  usage as the previous period. TARGET is set at 50% of period, which is the
  previous maximum. This provides smooth convergence for most repetitive IO
  patterns.

* Apply donation logic early at 20% budget. There's no risk in doing so as
  the calculation is based on the delta between the current budget and the
  target budget at the end of the coming period.

* Remove preemptive iocg activation for zero cost IOs. As donation can reach
  near zero now, the mere activation doesn't provide any protection anymore.
  In the unlikely case that this becomes a problem, the right solution is
  assigning appropriate costs for such IOs.

This significantly improves the donation determination logic while also
simplifying it. Now all donations are immediate, exact and smooth.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Andy Newell <newella@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-01 19:38:32 -06:00
Tejun Heo
e08d02aa5f blk-iocost: implement Andy's method for donation weight updates
iocost implements work conservation by reducing iocg->inuse and propagating
the adjustment upwards proportionally. However, while I knew the target
absolute hierarchical proportion - adjusted hweight_inuse, I couldn't figure
out how to determine the iocg->inuse adjustment to achieve that and
approximated the adjustment by scaling iocg->inuse using the proportion of
the needed hweight_inuse changes.

When nested, these scalings aren't accurate even when adjusting a single
node as the donating node also receives the benefit of the donated portion.
When multiple nodes are donating as they often do, they can be wildly wrong.

iocost employed various safety nets to combat the inaccuracies. There are
ample buffers in determining how much to donate, the adjustments are
conservative and gradual. While it can achieve a reasonable level of work
conservation in simple scenarios, the inaccuracies can easily add up leading
to significant loss of total work. This in turn makes it difficult to
closely cap vrate as vrate adjustment is needed to compensate for the loss
of work. The combination of inaccurate donation calculations and vrate
adjustments can lead to wide fluctuations and clunky overall behaviors.

Andy Newell devised a method to calculate the needed ->inuse updates to
achieve the target hweight_inuse's. The method is compatible with the
proportional inuse adjustment propagation which allows all hot path
operations to be local to each iocg.

To roughly summarize, Andy's method divides the tree into donating and
non-donating parts, calculates global donation rate which is used to
determine the target hweight_inuse for each node, and then derives per-level
proportions. There's non-trivial amount of math involved. Please refer to
the following pdfs for detailed descriptions.

  https://drive.google.com/file/d/1PsJwxPFtjUnwOY1QJ5AeICCcsL7BM3bo
  https://drive.google.com/file/d/1vONz1-fzVO7oY5DXXsLjSxEtYYQbOvsE
  https://drive.google.com/file/d/1WcrltBOSPN0qXVdBgnKm4mdp9FhuEFQN

This patch implements Andy's method in transfer_surpluses(). This makes the
donation calculations accurate per cycle and enables further improvements in
other parts of the donation logic.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Andy Newell <newella@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-01 19:38:32 -06:00
Tejun Heo
93f7d2db80 blk-iocost: restructure surplus donation logic
The way the surplus donation logic is structured isn't great. There are two
separate paths for starting/increasing donations and decreasing them making
the logic harder to follow and is prone to unnecessary behavior differences.

In preparation for improved donation handling, this patch restructures the
code so that

* All donors - new, increasing and decreasing - are funneled through the
  same code path.

* The target donation calculation is factored into hweight_after_donation()
  which is called once from the same spot for all possible donors.

* Actual inuse adjustment is factored into trasnfer_surpluses().

This change introduces a few behavior differences - e.g. donation amount
reduction now uses the max usage of the recent three periods just like new
and increasing donations, and inuse now gets adjusted upwards the same way
it gets downwards. These differences are unlikely to have severely negative
implications and the whole logic will be revamped soon.

This patch also removes two tracepoints. The existing TPs don't quite fit
the new implementation. A later patch will update and reinstate them.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-01 19:38:32 -06:00
Tejun Heo
065655c862 blk-iocost: decouple vrate adjustment from surplus transfers
Budget donations are inaccurate and could take multiple periods to converge.
To prevent triggering vrate adjustments while surplus transfers were
catching up, vrate adjustment was suppressed if donations were increasing,
which was indicated by non-zero nr_surpluses.

This entangling won't be necessary with the scheduled rewrite of donation
mechanism which will make it precise and immediate. Let's decouple the two
in preparation.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-01 19:38:32 -06:00
Tejun Heo
8692d2db8e blk-iocost: replace iocg->has_surplus with ->surplus_list
Instead of marking iocgs with surplus with a flag and filtering for them
while walking all active iocgs, build a surpluses list. This doesn't make
much difference now but will help implementing improved donation logic which
will iterate iocgs with surplus multiple times.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-01 19:38:32 -06:00
Tejun Heo
1aa50d020c blk-iocost: calculate iocg->usages[] from iocg->local_stat.usage_us
Currently, iocg->usages[] which are used to guide inuse adjustments are
calculated from vtime deltas. This, however, assumes that the hierarchical
inuse weight at the time of calculation held for the entire period, which
often isn't true and can lead to significant errors.

Now that we have absolute usage information collected, we can derive
iocg->usages[] from iocg->local_stat.usage_us so that inuse adjustment
decisions are made based on actual absolute usage. The calculated usage is
clamped between 1 and WEIGHT_ONE and WEIGHT_ONE is also used to signal
saturation regardless of the current hierarchical inuse weight.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-01 19:38:32 -06:00
Tejun Heo
97eb19751f blk-iocost: add absolute usage stat
Currently, iocost doesn't collect or expose any statistics punting off all
monitoring duties to drgn based iocost_monitor.py. While it works for some
scenarios, there are some usability and data availability challenges. For
example, accurate per-cgroup usage information can't be tracked by vtime
progression at all and the number available in iocg->usages[] are really
short-term snapshots used for control heuristics with possibly significant
errors.

This patch implements per-cgroup absolute usage stat counter and exposes it
through io.stat along with the current vrate. Usage stat collection and
flushing employ the same method as cgroup rstat on the active iocg's and the
only hot path overhead is preemption toggling and adding to a percpu
counter.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-01 19:38:32 -06:00
Tejun Heo
da437b95db blk-iocost: grab ioc->lock for debt handling
Currently, debt handling requires only iocg->waitq.lock. In the future, we
want to adjust and propagate inuse changes depending on debt status. Let's
grab ioc->lock in debt handling paths in preparation.

* Because ioc->lock nests outside iocg->waitq.lock, the decision to grab
  ioc->lock needs to be made before entering the critical sections.

* Add and use iocg_[un]lock() which handles the conditional double locking.

* Add @pay_debt to iocg_kick_waitq() so that debt payment happens only when
  the caller grabbed both locks.

This patch is prepatory and the comments contain references to future
changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-01 19:38:32 -06:00
Tejun Heo
7ca5b2e60b blk-iocost: streamline vtime margin and timer slack handling
The margin handling was pretty inconsistent.

* ioc->margin_us and ioc->inuse_margin_vtime were used as vtime margin
  thresholds. However, the two are in different units with the former
  requiring conversion to vtime on use.

* iocg_kick_waitq() was using a quarter of WAITQ_TIMER_MARGIN_PCT of
  period_us as the timer slack - ~1.2%. While iocg_kick_delay() was using a
  quarter of ioc->margin_us - ~12.5%. There aren't strong reasons to use
  different values for the two.

This patch cleans up margin and timer slack handling:

* vtime margins are now recorded in ioc->margins.{min, max} on period
  duration changes and used consistently.

* Timer slack is now 1% of period_us and recorded in ioc->timer_slack_ns and
  used consistently for iocg_kick_waitq() and iocg_kick_delay().

The only functional change is shortening of timer slack. No meaningful
visible change is expected.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-01 19:38:32 -06:00
Tejun Heo
ce95570acf blk-iocost: make ioc_now->now and ioc->period_at 64bit
They are in microseconds and wrap in around 1.2 hours with u32. While
unlikely, confusions from wraparounds are still possible. We aren't saving
anything meaningful by keeping these u32. Let's make them u64.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-01 19:38:32 -06:00