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From: Zefan Li <lizefan@huawei.com>
To: Tejun Heo <tj@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>, <cgroups@vger.kernel.org>,
	<mingo@redhat.com>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/3] sched, cgroup: replace signal_struct->group_rwsem with a global percpu_rwsem
Date: Sun, 24 May 2015 10:35:48 +0800	[thread overview]
Message-ID: <55613904.7060502@huawei.com> (raw)
In-Reply-To: <20150521203943.GS24861@htj.duckdns.org>

On 2015/5/22 4:39, Tejun Heo wrote:
> Hello, Li.
> 
> On Wed, May 20, 2015 at 06:05:37PM +0800, Zefan Li wrote:
>>> The latency is bound by synchronize_sched_expedited().  Given the way
>>> cgroups are used in majority of setups (process migration happening
>>> only during service / session setups), I think this should be okay.
>>
>> Actually process migration can happen quite frequently, for example in
>> Android phones, and that's why Google had an out-of-tree patch to remove
>> the synchronize_rcu() in that path, which turned out to be buggy.
> 
> It's still not a very frequent operation tho.  We're talking about
> users switching fore/background jobs here and the expedited
> synchronization w/ preemption enabled doesn't take much time.  In
> addition, as it currently stands, android is doing memory charge
> immigration on each fore/background switches.  I'm pretty doubtful
> this would make any difference.
> 

I did some testing with my laptop.

Moving a task between 2 cgroups for 10W times with one or two threads:

                  1T        2T
orig              3.36s     3.65s
orig+tj           3.55s     6.31s
orig+sync_rcu     16.69s    28.47s    (only 1000 times)

The overhead looks acceptable.

WARNING: multiple messages have this Message-ID (diff)
From: Zefan Li <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
To: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Cc: Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>,
	cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH 2/3] sched, cgroup: replace signal_struct->group_rwsem with a global percpu_rwsem
Date: Sun, 24 May 2015 10:35:48 +0800	[thread overview]
Message-ID: <55613904.7060502@huawei.com> (raw)
In-Reply-To: <20150521203943.GS24861-piEFEHQLUPpN0TnZuCh8vA@public.gmane.org>

On 2015/5/22 4:39, Tejun Heo wrote:
> Hello, Li.
> 
> On Wed, May 20, 2015 at 06:05:37PM +0800, Zefan Li wrote:
>>> The latency is bound by synchronize_sched_expedited().  Given the way
>>> cgroups are used in majority of setups (process migration happening
>>> only during service / session setups), I think this should be okay.
>>
>> Actually process migration can happen quite frequently, for example in
>> Android phones, and that's why Google had an out-of-tree patch to remove
>> the synchronize_rcu() in that path, which turned out to be buggy.
> 
> It's still not a very frequent operation tho.  We're talking about
> users switching fore/background jobs here and the expedited
> synchronization w/ preemption enabled doesn't take much time.  In
> addition, as it currently stands, android is doing memory charge
> immigration on each fore/background switches.  I'm pretty doubtful
> this would make any difference.
> 

I did some testing with my laptop.

Moving a task between 2 cgroups for 10W times with one or two threads:

                  1T        2T
orig              3.36s     3.65s
orig+tj           3.55s     6.31s
orig+sync_rcu     16.69s    28.47s    (only 1000 times)

The overhead looks acceptable.

  reply	other threads:[~2015-05-24  2:36 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-05-13 20:35 [PATCHSET] cgroup, sched: restructure threadgroup locking and replace it with a percpu_rwsem Tejun Heo
2015-05-13 20:35 ` Tejun Heo
2015-05-13 20:35 ` [PATCH 1/3] sched, cgroup: reorganize threadgroup locking Tejun Heo
2015-05-13 20:35   ` Tejun Heo
2015-05-14  1:09   ` Sergey Senozhatsky
2015-05-14  1:09     ` Sergey Senozhatsky
2015-05-14 15:17     ` Tejun Heo
2015-05-14 15:17       ` Tejun Heo
2015-05-13 20:35 ` [PATCH 2/3] sched, cgroup: replace signal_struct->group_rwsem with a global percpu_rwsem Tejun Heo
2015-05-19 15:16   ` Peter Zijlstra
2015-05-19 15:51     ` Tejun Heo
2015-05-19 15:51       ` Tejun Heo
2015-05-20 10:05       ` Zefan Li
2015-05-20 10:05         ` Zefan Li
2015-05-21 20:39         ` Tejun Heo
2015-05-21 20:39           ` Tejun Heo
2015-05-24  2:35           ` Zefan Li [this message]
2015-05-24  2:35             ` Zefan Li
2015-05-13 20:35 ` [PATCH 3/3] cgroup: simplify threadgroup locking Tejun Heo
2015-05-18 16:34 ` [PATCHSET] cgroup, sched: restructure threadgroup locking and replace it with a percpu_rwsem Tejun Heo
2015-05-18 16:34   ` Tejun Heo
2015-05-18 20:06   ` Peter Zijlstra
2015-05-18 20:06     ` Peter Zijlstra
2015-05-27  0:34 ` Tejun Heo
2015-05-27  0:34   ` Tejun Heo

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