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| author | Tejun Heo <tj@kernel.org> | 2015-09-16 12:53:17 -0400 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2015-09-16 12:53:17 -0400 |
| commit | 1ed1328792ff46e4bb86a3d7f7be2971f4549f6c (patch) | |
| tree | 53719cfc0bf81bc7e6fb522944553d9b4fa36cbf /include/linux/sched.h | |
| parent | 0c986253b939cc14c69d4adbe2b4121bdf4aa220 (diff) | |
| download | lwn-1ed1328792ff46e4bb86a3d7f7be2971f4549f6c.tar.gz lwn-1ed1328792ff46e4bb86a3d7f7be2971f4549f6c.zip | |
sched, cgroup: replace signal_struct->group_rwsem with a global percpu_rwsem
Note: This commit was originally committed as d59cfc09c32a but got
reverted by 0c986253b939 due to the performance regression from
the percpu_rwsem write down/up operations added to cgroup task
migration path. percpu_rwsem changes which alleviate the
performance issue are pending for v4.4-rc1 merge window.
Re-apply.
The cgroup side of threadgroup locking uses signal_struct->group_rwsem
to synchronize against threadgroup changes. This per-process rwsem
adds small overhead to thread creation, exit and exec paths, forces
cgroup code paths to do lock-verify-unlock-retry dance in a couple
places and makes it impossible to atomically perform operations across
multiple processes.
This patch replaces signal_struct->group_rwsem with a global
percpu_rwsem cgroup_threadgroup_rwsem which is cheaper on the reader
side and contained in cgroups proper. This patch converts one-to-one.
This does make writer side heavier and lower the granularity; however,
cgroup process migration is a fairly cold path, we do want to optimize
thread operations over it and cgroup migration operations don't take
enough time for the lower granularity to matter.
Signed-off-by: Tejun Heo <tj@kernel.org>
Link: http://lkml.kernel.org/g/55F8097A.7000206@de.ibm.com
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Diffstat (limited to 'include/linux/sched.h')
| -rw-r--r-- | include/linux/sched.h | 12 |
1 files changed, 0 insertions, 12 deletions
diff --git a/include/linux/sched.h b/include/linux/sched.h index b7b9501b41af..a4ab9daa387c 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -762,18 +762,6 @@ struct signal_struct { unsigned audit_tty_log_passwd; struct tty_audit_buf *tty_audit_buf; #endif -#ifdef CONFIG_CGROUPS - /* - * group_rwsem prevents new tasks from entering the threadgroup and - * member tasks from exiting,a more specifically, setting of - * PF_EXITING. fork and exit paths are protected with this rwsem - * using threadgroup_change_begin/end(). Users which require - * threadgroup to remain stable should use threadgroup_[un]lock() - * which also takes care of exec path. Currently, cgroup is the - * only user. - */ - struct rw_semaphore group_rwsem; -#endif oom_flags_t oom_flags; short oom_score_adj; /* OOM kill score adjustment */ |