From 1ed1328792ff46e4bb86a3d7f7be2971f4549f6c Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Wed, 16 Sep 2015 12:53:17 -0400 Subject: 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 Link: http://lkml.kernel.org/g/55F8097A.7000206@de.ibm.com Cc: Ingo Molnar Cc: Peter Zijlstra --- include/linux/sched.h | 12 ------------ 1 file changed, 12 deletions(-) (limited to 'include/linux/sched.h') 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 */ -- cgit v1.2.3