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

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Date:	Thu, 05 Jul 2007 15:22:29 -0400
From:	Bill Davidsen <davidsen@....com>
To:	Michael Tokarev <mjt@....msk.ru>
CC:	Tejun Heo <htejun@...il.com>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-ide@...r.kernel.org, linux-scsi@...r.kernel.org
Subject: Re: Some NCQ numbers...

Michael Tokarev wrote:
> Tejun Heo wrote:
>> 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.
> 
> Here are actual results - the tests were still running when
> I replied yesterday.
> 
> Again, this is Seagate ST3250620AS "desktop" drive, 7200RPM,
> 16Mb cache, 250Gb capacity.  The tests were performed with
> queue depth = 64 (on mptsas), drive write cache is turned
> off.
> 
But... with write cache off you don't let the drive do some things which 
might show a lot of improvement with one scheduler or another. So your 
data are only part of the story, aren't they?

[snip]

>>> 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.
> 
> Sure thing.  I guess I'll set up a web page with all
> the results so far, in a hope someday it will be more
> complete (we don't have many different drives to test,
> but others do).
> 
> By the way.  Both SATA drives we have are single-platter
> ones (with 500Gb models they've 2 platters, and 750Gb
> ones are with 3 platters), while all SCSI drives I
> tested have more than one platters.  Maybe this is
> yet another reason for NCQ failing.
> 
> And another note.  I heard somewhere that Seagate for
> one prohibits publishing of tests like this, however
> I haven't signed any NDAs and somesuch when purchased
> their drives in a nearest computer store... ;)
> 
>>> 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.
> 
> Oh well, I see.... :(
> 

-- 
Bill Davidsen <davidsen@....com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot
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