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Date: Wed, 13 Aug 2014 19:53:28 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Rik van Riel <riel@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>, linux-kernel@vger.kernel.org,
        Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>,
        Frank Mayhar <fmayhar@google.com>,
        Frederic Weisbecker <fweisbec@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Sanjay Rao <srao@redhat.com>, Larry Woodman <lwoodman@redhat.com>
Subject: Re: [PATCH RFC] time: drop do_sys_times spinlock
Message-ID: <20140813175328.GY9918@twins.programming.kicks-ass.net>
References: <20140812142539.01851e52@annuminas.surriel.com>
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On Wed, Aug 13, 2014 at 01:50:24PM -0400, Rik van Riel wrote:
> On 08/13/2014 01:40 PM, Peter Zijlstra wrote:
>=20
> > 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.
>=20
> 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.
>=20
> read_seqbegin_or_lock would do the trick...

Yep that would work.

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