path: root/kernel/fork.c
diff options
authorTejun Heo <>2015-09-16 12:53:17 -0400
committerTejun Heo <>2015-09-16 12:53:17 -0400
commit1ed1328792ff46e4bb86a3d7f7be2971f4549f6c (patch)
tree53719cfc0bf81bc7e6fb522944553d9b4fa36cbf /kernel/fork.c
parent0c986253b939cc14c69d4adbe2b4121bdf4aa220 (diff)
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: Cc: Ingo Molnar <> Cc: Peter Zijlstra <>
Diffstat (limited to 'kernel/fork.c')
1 files changed, 0 insertions, 4 deletions
diff --git a/kernel/fork.c b/kernel/fork.c
index 2845623fb582..7d5f0f118a63 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1149,10 +1149,6 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
- init_rwsem(&sig->group_rwsem);
sig->oom_score_adj = current->signal->oom_score_adj;
sig->oom_score_adj_min = current->signal->oom_score_adj_min;