linux-kernel - Re: [2.6 patch] make I/O schedulers non-modular

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Message-Id: <20071125211259.c69040fa.akpm@linux-foundation.org>
Date:	Sun, 25 Nov 2007 21:12:59 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Al Boldi <a1426z@...ab.com>
Cc:	linux-kernel@...r.kernel.org, Adrian Bunk <bunk@...sta.de>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [2.6 patch] make I/O schedulers non-modular


(cc's lovingly restored.  Please do not do that)

On Mon, 26 Nov 2007 07:57:00 +0300 Al Boldi <a1426z@...ab.com> wrote:

> Jens Axboe wrote:
> > On Sun, Nov 25 2007, Adrian Bunk wrote:
> > > Is there any technical reason why we need 4 different schedulers at all?
> >
> > Until we have the perfect scheduler :-)
> >
> > With some hard work and testing, we should be able to get rid of 'as'.
> > It still beats cfq for some of the workloads that deadline is good at,
> > so not quite yet.
> >
> > > I have the gut feeling that the usual thing happens and people e.g. not
> > > report some cfq problems because as works for them...
> >
> > There's always a risk with "duplicate", like several drivers for the
> > same hardware. I'm not disputing that.
> 
> Actually, both 'cfq' and 'as' are broken, and have been repeatedly reported 
> as such.  Deadline is the only one that currently looks sane, and seems like 
> a good starting point for a more involved iosched.  But keep in mind, the 
> fact that 'cfq' and 'as' are broken may also point to a lower-level block-io 
> problem.  So, incrementally improving deadline may help discovering the 
> problems both 'cfq' and 'as' are plagued with.
> 

Sorry, but these are vague and unuseful assertions.

Please send bug reports, preferably with testcases which developers can use
when fixing the bugs.
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