Re: Some NCQ numbers...

Tejun Heo wrote:

Hello,

Michael Tokarev wrote:

quoted

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.

noop scheduler:

BlkSz Trd linRd rndRd linWr rndWr  rndR/W
   4k   1  12.8   0.3   0.4   0.3   0.1/ 0.1
        4         0.3         0.3   0.1/ 0.1
       32         0.3         0.3   0.1/ 0.1
   8k   1  24.6   0.6   0.9   0.6   0.3/ 0.3
        4         0.6         0.6   0.3/ 0.3
       32         0.6         0.6   0.3/ 0.3
  16k   1  41.3   1.2   1.8   1.1   0.6/ 0.6
        4         1.2         1.1   0.6/ 0.6
       32         1.2         1.1   0.6/ 0.6
  32k   1  58.4   2.2   3.5   2.1   1.1/ 1.1
        4         2.3         2.1   1.1/ 1.1
       32         2.3         2.1   1.1/ 1.1
 128k   1  80.4   8.1  12.5   7.2   3.8/ 3.8
        4         8.1         7.2   3.8/ 3.8
       32         8.1         7.2   3.8/ 3.8
1024k   1  80.5  33.9  33.8  24.5  14.3/14.3
        4        34.1        24.6  14.3/14.2
       32        34.2        24.6  14.4/14.2

deadline scheduler:

BlkSz Trd linRd rndRd linWr rndWr  rndR/W
   4k   1  12.8   0.3   0.4   0.3   0.1/ 0.1
        4         0.3         0.3   0.1/ 0.1
       32         0.3         0.3   0.1/ 0.1
   8k   1  24.5   0.6   0.9   0.6   0.3/ 0.3
        4         0.6         0.6   0.3/ 0.3
       32         0.6         0.6   0.3/ 0.3
  16k   1  41.3   1.2   1.8   1.1   0.6/ 0.6
        4         1.2         1.1   0.6/ 0.6
       32         1.2         1.1   0.6/ 0.6
  32k   1  57.7   2.3   3.4   2.1   1.1/ 1.1
        4         2.3         2.1   1.1/ 1.1
       32         2.3         2.1   1.1/ 1.1
 128k   1  79.4   8.1  12.5   7.2   3.8/ 3.8
        4         8.1         7.3   3.8/ 3.8
       32         8.2         7.3   3.9/ 3.8
1024k   1  79.4  33.7  33.8  24.5  14.2/14.2
        4        33.9        24.6  14.3/14.2
       32        33.4        24.4  17.0/10.5

[]

quoted

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... ;)

quoted

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.... :(

/mjt