linux-kernel - Re: Some NCQ numbers...

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Message-ID: <468AB1A7.9010201@msgid.tls.msk.ru>
Date:	Wed, 04 Jul 2007 00:29:27 +0400
From:	Michael Tokarev <mjt@....msk.ru>
To:	Tejun Heo <htejun@...il.com>
CC:	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-ide@...r.kernel.org, linux-scsi@...r.kernel.org
Subject: Re: Some NCQ numbers...

Tejun Heo wrote:
> Michael Tokarev wrote:
[]
>> A test drive is Seagate Barracuda ST3250620AS "desktop" drive,
>> 250Gb, cache size is 16Mb, 7200RPM.
[test shows that NCQ makes no difference whatsoever]

> And which elevator?

Well.  It looks like the results does not depend on the
elevator.  Originally I tried with deadline, and just
re-ran the test with noop (hence the long delay with
the answer) - changing linux elevator changes almost
nothing in the results - modulo some random "fluctuations".

In any case, NCQ - at least in this drive - just does
not work.  Linux with its I/O elevator may help to
speed things up a bit, but the disk does nothing in
this area.  NCQ doesn't slow things down either - it
just does not work.

The same's for ST3250620NS "enterprise" drives.

By the way, Seagate announced Barracuda ES 2 series
(in range 500..1200Gb if memory serves) - maybe with
those, NCQ will work better?

Or maybe it's libata which does not implement NCQ
"properly"?  (As I shown before, with almost all
ol'good SCSI drives TCQ helps alot - up to 2x the
difference and more - with multiple I/O threads)

/mjt
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