linux-kernel - Re: [PATCH] cfq: fix IOPRIO_CLASS

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Message-ID: <20071107125057.GF5525@kernel.dk>
Date:	Wed, 7 Nov 2007 13:50:57 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, Nick <gentuu@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cfq: fix IOPRIO_CLASS_IDLE delays

On Wed, Nov 07 2007, Oleg Nesterov wrote:
> On 11/06, Jens Axboe wrote:
> >
> > On Tue, Nov 06 2007, Oleg Nesterov wrote:
> > >
> > > (I guess this patch is not complete, overflow is still possible)
> >
> > Hmm, where would it overflow?
> 
> What if the queue was idle long enough (no !CLASS_IDLE requests) so that
> jiffies wraps into the past wrt ->last_end_request?
> 
> IOW, perhaps something like the patch below makes some sense. Of course,
> this is only a theoretical problem, I'm not sure we really need a fix.

OK I see what you mean, probably pretty much a theoretical problem only.
But that doesn't mean it should be fixed, I've applied your patch. It
also collects the two paths enabling the idle class timer, so I consider
it a cleanup as well as it improves readability.

-- 
Jens Axboe

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