From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Dmitry Shmidt <dimitrysh@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
John Stultz <john.stultz@linaro.org>, Tejun Heo <tj@kernel.org>,
Ingo Molnar <mingo@redhat.com>,
lkml <linux-kernel@vger.kernel.org>,
Rom Lemarchand <romlem@google.com>,
Colin Cross <ccross@google.com>, Todd Kjos <tkjos@google.com>,
Oleg Nesterov <oleg@redhat.com>
Subject: Re: Severe performance regression w/ 4.4+ on Android due to cgroup locking changes
Date: Wed, 13 Jul 2016 11:32:23 -0700 [thread overview]
Message-ID: <20160713183223.GL7094@linux.vnet.ibm.com> (raw)
In-Reply-To: <CAH7ZN-wPpdn6qjf_POYkrqB9c8AJ95RAgj0heSXmtKjuWDHHrg@mail.gmail.com>
On Wed, Jul 13, 2016 at 11:13:26AM -0700, Dmitry Shmidt wrote:
> On Wed, Jul 13, 2016 at 7:42 AM, Paul E. McKenney
> <paulmck@linux.vnet.ibm.com> wrote:
> > On Wed, Jul 13, 2016 at 10:21:12AM +0200, Peter Zijlstra wrote:
> >> On Tue, Jul 12, 2016 at 05:00:04PM -0700, John Stultz wrote:
> >> > Hey Tejun,
> >> >
> >> > So Dmitry Shmidt recently noticed that with 4.4 based systems we're
> >> > seeing quite a bit of performance overhead from
> >> > __cgroup_procs_write().
> >> >
> >> > With 4.4 tree as it stands, we're seeing __cgroup_procs_write() quite
> >> > often take 10s of miliseconds to execute (with max times up in the
> >> > 80ms range).
> >> >
> >> > While with 4.1 it was quite often in the single usec range, and max
> >> > time values still in in sub-milisecond range.
> >> >
> >> > The majority of these performance regressions seem to come from the
> >> > locking changes in:
> >> >
> >> > 3014dde762f6 ("cgroup: simplify threadgroup locking")
> >> > and
> >> > 1ed1328792ff ("sched, cgroup: replace signal_struct->group_rwsem with
> >> > a global percpu_rwsem")
> >> >
> >> > Dmitry has found that by reverting these two changes (which don't
> >> > revert easiliy), we can get back down to tens 10-100 usec range for
> >> > most calls, with max values occasionally spiking to ~18ms.
> >> >
> >> > Those two commits do talk about performance regressions, that were
> >> > supposedly alleviated by percpu_rwsem changes, but I'm not sure we are
> >> > seeing this.
> >>
> >> Do you have 'funny' RCU options that quickly force a grace period when
> >> you go idle or something?
> >>
> >> But yes, it does not surprise me to find this commit is causing
> >> problems.
> >
> > Hmmm... Looks like RCU is present both before and after. But please
> > do send along your .config.
>
> Attached
No funny RCU Kconfig options set -- vanilla preemptible RCU.
> > Speaking of .config, is CONFIG_PREEMPT=y? If so, does the workload
> > feature preemption and migration? If that is the case, you might be
> > seeing contention on the per-CPU cgroup_threadgroup_rwsem, given that
> > the second patch seems to be adding acquisitions.
>
> CONFIG_PREEMPT=y is set.
> We see this issue during the boot, so it supposes to be enough CPU load to
> cause preemption and migration.
How early during boot? Presumably after the scheduler has started...
Thanx, Paul
next prev parent reply other threads:[~2016-07-13 18:32 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-13 0:00 Severe performance regression w/ 4.4+ on Android due to cgroup locking changes John Stultz
2016-07-13 8:21 ` Peter Zijlstra
2016-07-13 14:42 ` Paul E. McKenney
2016-07-13 18:13 ` Dmitry Shmidt
2016-07-13 18:32 ` Paul E. McKenney [this message]
2016-07-13 18:21 ` Tejun Heo
2016-07-13 18:33 ` Tejun Heo
2016-07-13 20:13 ` John Stultz
2016-07-13 20:18 ` Tejun Heo
2016-07-13 20:26 ` Peter Zijlstra
2016-07-13 20:39 ` Tejun Heo
2016-07-13 20:51 ` Peter Zijlstra
2016-07-13 21:01 ` Tejun Heo
2016-07-13 21:03 ` Paul E. McKenney
2016-07-13 21:05 ` Tejun Heo
2016-07-13 21:18 ` Paul E. McKenney
2016-07-13 21:42 ` Paul E. McKenney
2016-07-13 21:46 ` John Stultz
2016-07-13 22:17 ` Paul E. McKenney
2016-07-13 22:39 ` John Stultz
2016-07-13 23:02 ` Paul E. McKenney
2016-07-13 23:04 ` Paul E. McKenney
2016-07-14 11:35 ` Tejun Heo
2016-07-14 12:04 ` Peter Zijlstra
2016-07-14 12:08 ` Tejun Heo
2016-07-14 12:20 ` Peter Zijlstra
2016-07-14 15:07 ` Tejun Heo
2016-07-14 15:24 ` Tejun Heo
2016-07-14 16:32 ` Peter Zijlstra
2016-07-14 17:34 ` Oleg Nesterov
2016-07-14 16:54 ` John Stultz
2016-07-13 22:25 ` John Stultz
2016-07-13 22:01 ` Tejun Heo
2016-07-13 22:33 ` Paul E. McKenney
2016-07-14 6:49 ` Peter Zijlstra
2016-07-14 11:20 ` Tejun Heo
2016-07-14 12:11 ` Peter Zijlstra
2016-07-14 15:14 ` Tejun Heo
2016-07-14 13:18 ` Peter Zijlstra
2016-07-14 14:14 ` Peter Zijlstra
2016-07-14 14:58 ` Oleg Nesterov
2016-07-14 16:14 ` Peter Zijlstra
2016-07-14 16:37 ` Peter Zijlstra
2016-07-14 17:05 ` Oleg Nesterov
2016-07-14 16:23 ` Paul E. McKenney
2016-07-14 16:45 ` Peter Zijlstra
2016-07-14 17:15 ` Paul E. McKenney
2016-07-14 16:43 ` John Stultz
2016-07-14 16:49 ` Peter Zijlstra
2016-07-14 17:02 ` John Stultz
2016-07-14 17:13 ` Oleg Nesterov
2016-07-14 17:30 ` John Stultz
2016-07-14 17:41 ` Oleg Nesterov
2016-07-14 17:51 ` John Stultz
2016-07-14 18:09 ` Oleg Nesterov
2016-07-14 18:36 ` Peter Zijlstra
2016-07-14 19:35 ` Peter Zijlstra
2016-07-13 20:57 ` John Stultz
2016-07-13 20:52 ` Paul E. McKenney
2016-07-13 20:57 ` Peter Zijlstra
2016-07-13 21:08 ` Paul E. McKenney
2016-07-13 21:01 ` Dmitry Shmidt
2016-07-13 21:03 ` John Stultz
2016-07-13 21:05 ` Paul E. McKenney
2016-07-13 20:31 ` Dmitry Shmidt
2016-07-13 20:44 ` Colin Cross
2016-07-13 20:54 ` Tejun Heo
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