linux-kernel - Re: [PATCH 2/3] relay: Fix race condition which occurs when reading across CPUs.

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Message-ID: <84144f020806161118n70a876aeyb5ccac7b1e21d842@mail.gmail.com>
Date:	Mon, 16 Jun 2008 21:18:11 +0300
From:	"Pekka Enberg" <penberg@...helsinki.fi>
To:	"Jens Axboe" <jens.axboe@...cle.com>
Cc:	"Eduard - Gabriel Munteanu" <eduard.munteanu@...ux360.ro>,
	"Mathieu Desnoyers" <compudj@...stal.dyndns.org>,
	"Tom Zanussi" <tzanussi@...il.com>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, righi.andrea@...il.com
Subject: Re: [PATCH 2/3] relay: Fix race condition which occurs when reading across CPUs.

Hi Jens,

On Mon, Jun 16 2008, Eduard - Gabriel Munteanu wrote:
>> In any case, if we use relay in a hot path, we are doing debugging, so
>> a couple of atomic operations won't be a big problem. Along with
>> setting affinity, this shouldn't be a problem.

On Mon, Jun 16, 2008 at 7:46 PM, Jens Axboe <jens.axboe@...cle.com> wrote:
> Ehm no, that is a completely false claim. Relay speed does matter, a
> great deal. We rely heavily on eg blktrace being as ligt weight as
> possible to capture millions of events in a very short time frame
> without impacting performance too much. Relay is NOT just for debugging.
>
> So I completely agree with Mathieu here, and I'm not a big fan of the
> proposed solution.

OK, so we just document that fact that you're not supposed to read
from different CPU and be done with that? Or do you have any
alternative fix in mind?
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