linux-kernel - Re: [PATCH RFC] time: drop do_sys

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Message-ID: <53EBA560.8030404@redhat.com>
Date:	Wed, 13 Aug 2014 13:50:24 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Oleg Nesterov <oleg@...hat.com>
CC:	linux-kernel@...r.kernel.org,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	Frank Mayhar <fmayhar@...gle.com>,
	Frederic Weisbecker <fweisbec@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sanjay Rao <srao@...hat.com>,
	Larry Woodman <lwoodman@...hat.com>
Subject: Re: [PATCH RFC] time: drop do_sys_times spinlock

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On 08/13/2014 01:40 PM, Peter Zijlstra wrote:

> So the problem with the above is the lack of fwd progress; if
> there's enough clone()/exit() happening in the thread group (and
> the more CPUs the more possible), we'll keep repeating.

We can fall back to taking the lock if we circle around,
or if there is a writer active when we are in seqcount_read,
similar to what the semaphore (ipc/sem.c) code is doing.

read_seqbegin_or_lock would do the trick...
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