linux-kernel - Re: 2.6.20-rc2+: CFQ halving disk throughput.

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Date:	Tue, 02 Jan 2007 10:01:31 -0500
From:	Mark Lord <lkml@....ca>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Rene Herman <rene.herman@...il.com>, Tejun Heo <htejun@...il.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org, Linus Torvalds <torvalds@...l.org>
Subject: Re: 2.6.20-rc2+: CFQ halving disk throughput.

Jens Axboe wrote:
>
>> But surely one of (not sure which) sync+async or async+sync may also be 
>> okay?
>> Or would it?
> 
> Async merge to sync request should be ok. But I wonder what happens with
> hdparm, since it seems to trigger one of these tests. Very puzzling.
> I'll dive in and take a look.

The code (written 10 years ago) isn't the best in the world,
and will be redone entirely for hdparm-7.0 this year.

But right now, it essentially does this:

loop:
	seek( to sector zero );
	read( 2MBytes );
	repeat loop for 3 seconds

Cheers
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