Davide Zini 2d31c684a0 block, bfq: inject I/O to underutilized actuators ... The main service scheme of BFQ for sync I/O is serving one sync bfq_queue at a time, for a while. In particular, BFQ enforces this scheme when it deems the latter necessary to boost throughput or to preserve service guarantees. Unfortunately, when BFQ enforces this policy, only one actuator at a time gets served for a while, because each bfq_queue contains I/O only for one actuator. The other actuators may remain underutilized. Actually, BFQ may serve (inject) extra I/O, taken from other bfq_queues, in parallel with that of the in-service queue. This injection mechanism may provide the ground for dealing also with the above actuator-underutilization problem. Yet BFQ does not take the actuator load into account when choosing which queue to pick extra I/O from. In addition, BFQ may happen to inject extra I/O only when the in-service queue is temporarily empty. In view of these facts, this commit extends the injection mechanism in such a way that the latter: (1) takes into account also the actuator load; (2) checks such a load on each dispatch, and injects I/O for an underutilized actuator, if there is one and there is I/O for it. To perform the check in (2), this commit introduces a load threshold, currently set to 4. A linear scan of each actuator is performed, until an actuator is found for which the following two conditions hold: the load of the actuator is below the threshold, and there is at least one non-in-service queue that contains I/O for that actuator. If such a pair (actuator, queue) is found, then the head request of that queue is returned for dispatch, instead of the head request of the in-service queue. We have set the threshold, empirically, to the minimum possible value for which an actuator is fully utilized, or close to be fully utilized. By doing so, injected I/O 'steals' as few drive-queue slots as possibile to the in-service queue. This reduces as much as possible the probability that the service of I/O from the in-service bfq_queue gets delayed because of slot exhaustion, i.e., because all the slots of the drive queue are filled with I/O injected from other queues (NCQ provides for 32 slots). This new mechanism also counters actuator underutilization in the case of asymmetric configurations of bfq_queues. Namely if there are few bfq_queues containing I/O for some actuators and many bfq_queues containing I/O for other actuators. Or if the bfq_queues containing I/O for some actuators have lower weights than the other bfq_queues. Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com> Signed-off-by: Paolo Valente <paolo.valente@linaro.org> Signed-off-by: Davide Zini <davidezini2@gmail.com> Link: https://lore.kernel.org/r/20230103145503.71712-8-paolo.valente@linaro.org Signed-off-by: Jens Axboe <axboe@kernel.dk>		2023-01-29 15:18:33 -07:00
..
partitions
badblocks.c
bdev.c
bfq-cgroup.c	block, bfq: inject I/O to underutilized actuators	2023-01-29 15:18:33 -07:00
bfq-iosched.c	block, bfq: inject I/O to underutilized actuators	2023-01-29 15:18:33 -07:00
bfq-iosched.h	block, bfq: inject I/O to underutilized actuators	2023-01-29 15:18:33 -07:00
bfq-wf2q.c	block, bfq: inject I/O to underutilized actuators	2023-01-29 15:18:33 -07:00
bio-integrity.c
bio.c
blk-cgroup-fc-appid.c
blk-cgroup-rwstat.c
blk-cgroup-rwstat.h
blk-cgroup.c	blk-cgroup: fix missing pd_online_fn() while activating policy	2023-01-16 19:04:07 -07:00
blk-cgroup.h
blk-core.c
blk-crypto-fallback.c
blk-crypto-internal.h
blk-crypto-profile.c
blk-crypto-sysfs.c
blk-crypto.c
blk-flush.c
blk-ia-ranges.c
blk-integrity.c
blk-ioc.c
blk-iocost.c
blk-iolatency.c
blk-ioprio.c
blk-ioprio.h
blk-lib.c
blk-map.c
blk-merge.c
blk-mq-cpumap.c
blk-mq-debugfs-zoned.c
blk-mq-debugfs.c
blk-mq-debugfs.h
blk-mq-pci.c
blk-mq-rdma.c
blk-mq-sched.c
blk-mq-sched.h
blk-mq-sysfs.c
blk-mq-tag.c
blk-mq-tag.h
blk-mq-virtio.c
blk-mq.c	block: fix hctx checks for batch allocation	2023-01-17 09:56:52 -07:00
blk-mq.h
blk-pm.c
blk-pm.h
blk-rq-qos.c
blk-rq-qos.h
blk-settings.c
blk-stat.c
blk-stat.h
blk-sysfs.c
blk-throttle.c
blk-throttle.h
blk-timeout.c
blk-wbt.c
blk-wbt.h
blk-zoned.c
blk.h
bounce.c
bsg-lib.c
bsg.c
disk-events.c
elevator.c
elevator.h
fops.c
genhd.c
holder.c
ioctl.c
ioprio.c
Kconfig
Kconfig.iosched
kyber-iosched.c
Makefile
mq-deadline.c
opal_proto.h
sed-opal.c
t10-pi.c