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SubjectRe: iowait problems on 2.6, not on 2.4
Date
On Thursday 27 May 2004 05:52, you wrote:
> Antonio Larrosa Jiménez <antlarr@tedial.com> wrote:
> > My next test will be to do the "dd tests" on one of the internal hard
> > disks and use it for the data instead of the external raid.
>
> That's a logical next step. The reduced read bandwith on the raid array
> should be fixed up before we can go any further. I don't recall any
> reports of qlogic fc-scsi performance regressions though.

Ok, let's analyze that first.

The dd tests gave the following results:

ext3 on the internal scsi HD:
2.4.21:
writing : 1m14s
reading : 1m2s
reading+writing : 2m16s
2.6.4:
writing : 1m19s
reading : 59s
reading+writing : 2m24s

reiserfs on the internal scsi HD:
2.4.21:
writing : 1m15s
reading : 1m1s
reading+writing : 2m22s
2.6.4:
writing : 1m19s
reading : 1m
reading+writing : 2m25s

ext3 on the raid using qlogic fc-scsi:
2.4.21:
writing : 30s
reading : 51s
reading+writing : 1m29s
2.6.4:
writing : 28s
reading : 1m26s
reading+writing : 2m19s

reiserfs on the raid using qlogic fc-scsi:
2.4.21:
writing : 37s
reading : 52s
reading+writing : 1m37s
2.6.4:
writing : 25s
reading : 1m27s
reading+writing : 2m3s

All the tests were made 3 times, and the average taken. In the cases where
there was too much variance, I repeated the tests some more times.

All the tests used 2Gb reads/writes (. I tried to make 8Gb reads/writes too,
but they got up to a minute variance (maybe the HD slowed itself down due to
temperature issues sometimes? I really don't know why this happened, but in
any case, I couldn't make reliable tests with files of that size).

So basically, there's no difference between 2.4.21 and 2.6.4 when using the
internal HD, but 2.6.4 is much slower when using the raid.
What I found strange is that writing to that raid is a bit faster on 2.6.4
while reading is much slower, which I suppose is what makes the difference.

So yes, I suppose there's a regression on the qlogic fc-scsi module.

Btw, the tests I timed were:

count=2048
write() { dd if=/dev/zero of=x bs=1M count=$count ; sync }
read() { dd if=x of=/dev/null bs=1M count=$count }
readwrite() { dd if=x of=y bs=1M count=$count ; sync }

In the case of read, I did the sync just before and after the timing, but
didn't include the sync inside the timed test.

As I said in my other mail, I can test any patch if needed.

Greetings and thanks for any help

--
Antonio Larrosa
Tecnologias Digitales Audiovisuales, S.L.
http://www.tedial.com
Parque Tecnologico de Andalucia . Málaga (Spain)
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