linux-kernel - Re: a bug in AS scheduler?

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Date:	Wed, 28 Feb 2007 14:34:58 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Benoit Boissinot <bboissin@...il.com>
Cc:	Xiaoning Ding <dingxn@....ohio-state.edu>,
	linux-kernel@...r.kernel.org
Subject: Re: a bug in AS scheduler?

On Wed, Feb 28 2007, Benoit Boissinot wrote:
> On 2/28/07, Jens Axboe <jens.axboe@...cle.com> wrote:
> >On Tue, Feb 27 2007, Xiaoning Ding wrote:
> >> Hi,
> >>
> >> I am reading the source code AS scheduler in 2.6.18(as-ioscheduler.c).
> >> In function as_close_req, variable delay is in millisecond, while
> >> ad->antic_expire is in jiffies. Doesn't the comparison of delay and
> >> ad->antic_expire make any problem?
> >> The related source code is quoted blow:
> >>
> >>       if (ad->antic_status == ANTIC_OFF || !ad->ioc_finished)
> >>               delay = 0;
> >>       else
> >>               delay = ((jiffies - ad->antic_start) * 1000) / HZ;
> >
> >antic_start is in jiffies, the difference is here multiplied by 1000 and
> >divided by HZ to turn it into msecs. so delay is in msecs.
> >
> I am pretty sure Xiaoning was talking about antic_expire, particularly
> this comparison:
> 
>     else if (delay <= 20 && delay <= ad->antic_expire)

Ah, I misread the name. That does look like a bug, antic_expire is in
jiffies.

-- 
Jens Axboe

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