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

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Message-ID: <40f323d00702280525g3d898a9bm1297dc32b8f7fda2@mail.gmail.com>
Date:	Wed, 28 Feb 2007 14:25:07 +0100
From:	"Benoit Boissinot" <bboissin@...il.com>
To:	"Jens Axboe" <jens.axboe@...cle.com>
Cc:	"Xiaoning Ding" <dingxn@....ohio-state.edu>,
	linux-kernel@...r.kernel.org
Subject: Re: a bug in AS scheduler?

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)

regards,

Benoit
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