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Chuck Lever af12deba53 NFSD: Optimize DRC bucket pruning 
[ Upstream commit 8847ecc927 ]

DRC bucket pruning is done by nfsd_cache_lookup(), which is part of
every NFSv2 and NFSv3 dispatch (ie, it's done while the client is
waiting).

I added a trace_printk() in prune_bucket() to see just how long
it takes to prune. Here are two ends of the spectrum:

 prune_bucket: Scanned 1 and freed 0 in 90 ns, 62 entries remaining
 prune_bucket: Scanned 2 and freed 1 in 716 ns, 63 entries remaining
...
 prune_bucket: Scanned 75 and freed 74 in 34149 ns, 1 entries remaining

Pruning latency is noticeable on fast transports with fast storage.
By noticeable, I mean that the latency measured here in the worst
case is the same order of magnitude as the round trip time for
cached server operations.

We could do something like moving expired entries to an expired list
and then free them later instead of freeing them right in
prune_bucket(). But simply limiting the number of entries that can
be pruned by a lookup is simple and retains more entries in the
cache, making the DRC somewhat more effective.

Comparison with a 70/30 fio 8KB 12 thread direct I/O test:

Before:

  write: IOPS=61.6k, BW=481MiB/s (505MB/s)(14.1GiB/30001msec); 0 zone resets

WRITE:
        1848726 ops (30%)
        avg bytes sent per op: 8340 avg bytes received per op: 136
        backlog wait: 0.635158  RTT: 0.128525   total execute time: 0.827242 (milliseconds)

After:

  write: IOPS=63.0k, BW=492MiB/s (516MB/s)(14.4GiB/30001msec); 0 zone resets

WRITE:
        1891144 ops (30%)
        avg bytes sent per op: 8340 avg bytes received per op: 136
        backlog wait: 0.616114  RTT: 0.126842   total execute time: 0.805348 (milliseconds)

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
2024-04-10 16:18:53 +02:00
arch x86/static_call: Add support for Jcc tail-calls 2024-04-10 16:18:49 +02:00
block block: Clear zone limits for a non-zoned stacked queue 2024-04-10 16:18:35 +02:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-22 14:22:01 +02:00
crypto crypto: api - Disallow identical driver names 2024-02-23 08:54:23 +01:00
Documentation docs: Document the FAN_FS_ERROR event 2024-04-10 16:18:52 +02:00
drivers x86/rfds: Mitigate Register File Data Sampling (RFDS) 2024-04-10 16:18:48 +02:00
fs NFSD: Optimize DRC bucket pruning 2024-04-10 16:18:53 +02:00
include NFS: Move NFS protocol display macros to global header 2024-04-10 16:18:52 +02:00
init modules: wait do_free_init correctly 2024-03-26 18:21:31 -04:00
io_uring io_uring: don't save/restore iowait state 2024-03-26 18:21:35 -04:00
ipc ipc/sem: Fix dangling sem_array access in semtimedop race 2022-12-08 11:28:45 +01:00
kernel fsnotify: clarify contract for create event hooks 2024-04-10 16:18:49 +02:00
lib arch: Introduce CONFIG_FUNCTION_ALIGNMENT 2024-04-10 16:18:49 +02:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm memtest: use {READ,WRITE}_ONCE in memory scanning 2024-04-10 16:18:42 +02:00
net xfrm: Avoid clang fortify warning in copy_to_user_tmpl() 2024-04-10 16:18:45 +02:00
samples samples/hw_breakpoint: fix building without module unloading 2023-09-23 11:10:01 +02:00
scripts kbuild: Move -Wenum-{compare-conditional,enum-conversion} into W=1 2024-04-10 16:18:41 +02:00
security landlock: Warn once if a Landlock action is requested while disabled 2024-04-10 16:18:39 +02:00
sound ALSA: hda/realtek - Fix headset Mic no show at resume back for Lenovo ALC897 platform 2024-04-10 16:18:45 +02:00
tools selftests/mqueue: Set timeout to 180 seconds 2024-04-10 16:18:35 +02:00
usr usr/include/Makefile: add linux/nfc.h to the compile-test coverage 2022-02-01 17:27:15 +01:00
virt KVM: Always flush async #PF workqueue when vCPU is being destroyed 2024-04-10 16:18:34 +02:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: add Andrej Shadura 2021-10-18 20:22:03 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS iio: stx104: Move to addac subdirectory 2023-08-26 14:23:27 +02:00
Makefile arch: Introduce CONFIG_FUNCTION_ALIGNMENT 2024-04-10 16:18:49 +02:00
README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.