Message-ID: <4DE7E279.9040300@fusionio.com>
Date: Thu, 2 Jun 2011 21:20:25 +0200
From: Jens Axboe <jaxboe@fusionio.com>
MIME-Version: 1.0
To: Jeff Moyer <jmoyer@redhat.com>
CC: "vgoyal@redhat.com" <vgoyal@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [patch/resend] iosched: prevent aliased requests from starving
  other I/O
References: <x49pqmwe5g0.fsf@segfault.boston.devel.redhat.com>
In-Reply-To: <x49pqmwe5g0.fsf@segfault.boston.devel.redhat.com>
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On 2011-06-02 15:19, Jeff Moyer wrote:
> Hi, Jens,
> 
> If you recall, I posted an RFC patch for this back in July of last year:
> http://lkml.org/lkml/2010/7/13/279
> 
> The basic problem is that a process can issue a never-ending stream of
> async direct I/Os to the same sector on a device, thus starving out
> other I/O in the system (due to the way the alias handling works in both
> cfq and deadline).  The solution I proposed back then was to start
> dispatching from the fifo after a certain number of aliases had been
> dispatched.  Vivek asked why we had to treat aliases differently at all,
> and I never had a good answer.  So, I put together a simple patch which
> allows aliases to be added to the rb tree (it adds them to the right,
> though that doesn't matter as the order isn't guaranteed anyway).  I
> think this is the preferred solution, as it doesn't break up time slices
> in CFQ or batches in deadline.  I've tested it, and it does solve the
> starvation issue.  Let me know what you think.

Thanks Jeff, applied to for-3.1/core

-- 
Jens Axboe

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