Date: Wed, 16 May 2007 02:08:12 +0400
From: Oleg Nesterov <oleg@tv-sign.ru>
To: Jarek Poplawski <jarkao2@o2.pl>
Cc: Tejun Heo <htejun@gmail.com>, Andrew Morton <akpm@linux-foundation.org>,
       David Chinner <dgc@sgi.com>, David Howells <dhowells@redhat.com>,
       Gautham Shenoy <ego@in.ibm.com>, Ingo Molnar <mingo@elte.hu>,
       Srivatsa Vaddagiri <vatsa@in.ibm.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] make cancel_rearming_delayed_work() reliable
Message-ID: <20070515220812.GB615@tv-sign.ru>
References: <464475EB.3000408@gmail.com> <20070511134714.GA191@tv-sign.ru> <46448965.7070500@gmail.com> <20070511145345.GA240@tv-sign.ru> <4645559D.4050602@gmail.com> <20070513192753.GA3014@tv-sign.ru> <46477239.9030007@gmail.com> <20070514194446.GA159@tv-sign.ru> <46496EC1.3090109@gmail.com> <20070515130904.GB3050@ff.dom.local>
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On 05/15, Jarek Poplawski wrote:
> 
> I've overheared somebody is talking about my favorite 2-nd bit!
> Probably I miss many points (your talk isn't the most clear),
> but I wonder if this bit couldn't be used otherwise: try_to_grab_
> sets the bit - others know cancel is pending, so don't disturb:
> e.g. insert_work doesn't queue (at least after works' cpu change,
> which seems to be the main problem here). Probably there is
> no reason to test this bit in all places - only in the most
> problematic; so, in insert_work maybe only after checking
> the cpu was changed. If this way is possible, we could avoid
> setting the VALID bit when not needed (no cancel pending). Maybe
> we could also think about some form of cooperation - e.g. clearing
> of this or other bit to ack the work was catched - of course
> this last thing could be too much, so not necessarily now.

We already discussed this... Surely, we can do this. I believe
this will complicate (and _imho_ uglify) the code too much.

May be I am wrong. Please provide a detailed description?

Oleg.

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