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

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Message-ID: <20140813175328.GY9918@twins.programming.kicks-ass.net>
Date:	Wed, 13 Aug 2014 19:53:28 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Rik van Riel <riel@...hat.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, 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

On Wed, Aug 13, 2014 at 01:50:24PM -0400, Rik van Riel wrote:
> 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...

Yep that would work.

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