Re: Some NCQ numbers...

Michael Tokarev wrote:

Tejun Heo wrote:

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Hello,

Michael Tokarev wrote:

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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]

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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... ;)

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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 [off-list ref]
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot