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

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Message-ID: <468AF5BB.10005@gmail.com>
Date:	Wed, 04 Jul 2007 10:19:55 +0900
From:	Tejun Heo <htejun@...il.com>
To:	Michael Tokarev <mjt@....msk.ru>
CC:	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-ide@...r.kernel.org, linux-scsi@...r.kernel.org
Subject: Re: Some NCQ numbers...

Hello,

Michael Tokarev wrote:
> 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".

I see.  Thanks for testing.

> 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?

No one would know without testing.

> 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)

Well, what the driver does is minimal.  It just passes through all the
commands to the harddrive.  After all, NCQ/TCQ gives the harddrive more
responsibility regarding request scheduling.

-- 
tejun
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