linux/kernel/cgroup
Tejun Heo d8ef4b38cb Revert "cgroup: Add memory barriers to plug cgroup_rstat_updated() race window"
This reverts commit 9a9e97b2f1 ("cgroup: Add memory barriers to plug
cgroup_rstat_updated() race window").

The commit was added in anticipation of memcg rstat conversion which needed
synchronous accounting for the event counters (e.g. oom kill count). However,
the conversion didn't get merged due to percpu memory overhead concern which
couldn't be addressed at the time.

Unfortunately, the patch's addition of smp_mb() to cgroup_rstat_updated()
meant that every scheduling event now had to go through an additional full
barrier and Mel Gorman noticed it as 1% regression in netperf UDP_STREAM test.

There's no need to have this barrier in tree now and even if we need
synchronous accounting in the future, the right thing to do is separating that
out to a separate function so that hot paths which don't care about
synchronous behavior don't have to pay the overhead of the full barrier. Let's
revert.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Mel Gorman <mgorman@techsingularity.net>
Link: http://lkml.kernel.org/r/20200409154413.GK3818@techsingularity.net
Cc: v4.18+
2020-04-09 14:55:46 -04:00
..
cgroup-internal.h fs_parse: fold fs_parameter_desc/fs_parameter_spec 2020-02-07 14:48:37 -05:00
cgroup-v1.c cgroup: Restructure release_agent_path handling 2020-03-12 16:44:35 -04:00
cgroup.c Merge branch 'for-5.7' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup 2020-04-03 11:30:20 -07:00
cpuset.c docs: cgroup-v1: Document the cpuset_v2_mode mount option 2020-04-03 11:42:56 -04:00
debug.c kernel: cgroup: fix misuse of %x 2019-05-06 08:47:48 -07:00
freezer.c cgroup: freezer: don't change task and cgroups status unnecessarily 2019-11-07 07:38:41 -08:00
legacy_freezer.c cgroup: rename freezer.c into legacy_freezer.c 2019-04-19 11:26:48 -07:00
Makefile cgroup: cgroup v2 freezer 2019-04-19 11:26:48 -07:00
namespace.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
pids.c clone3: allow spawning processes into cgroups 2020-02-12 17:57:51 -05:00
rdma.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 451 2019-06-19 17:09:08 +02:00
rstat.c Revert "cgroup: Add memory barriers to plug cgroup_rstat_updated() race window" 2020-04-09 14:55:46 -04:00