linux-kernel - Re: [PATCH v2] locking/percpu-rwsem: Optimize readers and reduce global impact

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Message-ID: <a720d3c9-b830-17b2-412b-549c4445d638@codeaurora.org>
Date:	Fri, 12 Aug 2016 18:44:28 -0700
From:	Om Dhyade <odhyade@...eaurora.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	John Stultz <john.stultz@...aro.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	lkml <linux-kernel@...r.kernel.org>, Tejun Heo <tj@...nel.org>,
	Dmitry Shmidt <dimitrysh@...gle.com>,
	Rom Lemarchand <romlem@...gle.com>,
	Colin Cross <ccross@...gle.com>, Todd Kjos <tkjos@...gle.com>
Subject: Re: [PATCH v2] locking/percpu-rwsem: Optimize readers and reduce
 global impact

Thank you Dimtry for sharing the patches.

Update from my tests:
Use-case: Android application launches.

I tested the patches on android N build, i see max latency ~7ms.
In my tests, the wait is due to: copy_process(fork.c) blocks all threads 
in __cgroup_procs_write including threads which are not part of the 
forking process's thread-group.

Dimtry had provided a hack patch which reverts to per-process rw-sem 
which had max latency of ~2ms.

android user-space binder library does 2 cgroup write operations per 
transaction, apart from the copy_process(fork.c) wait, i see pre-emption 
in _cgroup_procs_write causing waits.

Thanks.

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