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authorPeter Zijlstra <peterz@infradead.org>2016-08-11 18:54:13 +0200
committerIngo Molnar <mingo@kernel.org>2016-08-18 15:36:59 +0200
commit3942a9bd7b5842a924e99ee6ec1350b8006c94ec (patch)
treed3d768a716b040fabffe18b2c791c6eedfc11797 /include/linux/rcu_sync.h
parente8cb0fe6e7cc9b02bd97eae6efa8fe927fbfc905 (diff)
locking, rcu, cgroup: Avoid synchronize_sched() in __cgroup_procs_write()
The current percpu-rwsem read side is entirely free of serializing insns at the cost of having a synchronize_sched() in the write path. The latency of the synchronize_sched() is too high for cgroups. The commit 1ed1328792ff talks about the write path being a fairly cold path but this is not the case for Android which moves task to the foreground cgroup and back around binder IPC calls from foreground processes to background processes, so it is significantly hotter than human initiated operations. Switch cgroup_threadgroup_rwsem into the slow mode for now to avoid the problem, hopefully it should not be that slow after another commit: 80127a39681b ("locking/percpu-rwsem: Optimize readers and reduce global impact"). We could just add rcu_sync_enter() into cgroup_init() but we do not want another synchronize_sched() at boot time, so this patch adds the new helper which doesn't block but currently can only be called before the first use. Reported-by: John Stultz <john.stultz@linaro.org> Reported-by: Dmitry Shmidt <dimitrysh@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Colin Cross <ccross@google.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rom Lemarchand <romlem@google.com> Cc: Tejun Heo <tj@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Todd Kjos <tkjos@google.com> Link: http://lkml.kernel.org/r/20160811165413.GA22807@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/linux/rcu_sync.h')
-rw-r--r--include/linux/rcu_sync.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/rcu_sync.h b/include/linux/rcu_sync.h
index a63a33e6196e..ece7ed9a4a70 100644
--- a/include/linux/rcu_sync.h
+++ b/include/linux/rcu_sync.h
@@ -59,6 +59,7 @@ static inline bool rcu_sync_is_idle(struct rcu_sync *rsp)
}
extern void rcu_sync_init(struct rcu_sync *, enum rcu_sync_type);
+extern void rcu_sync_enter_start(struct rcu_sync *);
extern void rcu_sync_enter(struct rcu_sync *);
extern void rcu_sync_exit(struct rcu_sync *);
extern void rcu_sync_dtor(struct rcu_sync *);