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author | Michal Koutný <mkoutny@suse.com> | 2019-10-04 12:57:40 +0200 |
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committer | Tejun Heo <tj@kernel.org> | 2019-10-07 07:11:53 -0700 |
commit | 9a3284fad42f66bb43629c6716709ff791aaa457 (patch) | |
tree | 90ee5a200895f3be7b12fa1eff10fd1910afa019 /tools | |
parent | cgroup: Update comments about task exit path (diff) | |
download | linux-dev-9a3284fad42f66bb43629c6716709ff791aaa457.tar.xz linux-dev-9a3284fad42f66bb43629c6716709ff791aaa457.zip |
cgroup: Optimize single thread migration
There are reports of users who use thread migrations between cgroups and
they report performance drop after d59cfc09c32a ("sched, cgroup: replace
signal_struct->group_rwsem with a global percpu_rwsem"). The effect is
pronounced on machines with more CPUs.
The migration is affected by forking noise happening in the background,
after the mentioned commit a migrating thread must wait for all
(forking) processes on the system, not only of its threadgroup.
There are several places that need to synchronize with migration:
a) do_exit,
b) de_thread,
c) copy_process,
d) cgroup_update_dfl_csses,
e) parallel migration (cgroup_{proc,thread}s_write).
In the case of self-migrating thread, we relax the synchronization on
cgroup_threadgroup_rwsem to avoid the cost of waiting. d) and e) are
excluded with cgroup_mutex, c) does not matter in case of single thread
migration and the executing thread cannot exec(2) or exit(2) while it is
writing into cgroup.threads. In case of do_exit because of signal
delivery, we either exit before the migration or finish the migration
(of not yet PF_EXITING thread) and die afterwards.
This patch handles only the case of self-migration by writing "0" into
cgroup.threads. For simplicity, we always take cgroup_threadgroup_rwsem
with numeric PIDs.
This change improves migration dependent workload performance similar
to per-signal_struct state.
Signed-off-by: Michal Koutný <mkoutny@suse.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'tools')
0 files changed, 0 insertions, 0 deletions