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SubjectRe: iowait problems on 2.6, not on 2.4
Antonio Larrosa Jiménez <antlarr@tedial.com> wrote:
>
> 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:

Let me cc linux-scsi.

Guys: poke. Does anyone know why this:

The machine is a 4 cpu Pentium III (Cascades) system with four SCSI
SEAGATE ST336704 hard disks connected to an Adaptec AIC-7899P U160/m, and
a external RAID connected to a QLA2200/QLA2xxx FC-SCSI Host Bus Adapter.
The machine has 1Gb RAM.

got all slow at reads?


> 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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