Re: Where is the performance bottleneck?

[Holger Kiehl]

On Mon, 29 Aug 2005, Mark Hahn wrote:

> > The U320 SCSI controller has a 64 bit PCI-X bus for itself, there is no other
> > device on that bus. Unfortunatly I was unable to determine at what speed
> > it is running, here the output from lspci -vv:
> ...
> >                  Status: Bus=2 Dev=4 Func=0 64bit+ 133MHz+ SCD- USC-, DC=simple,
>
> the "133MHz+" is a good sign.  OTOH the latency (72) seems rather low - my
> understanding is that that would noticably limit the size of burst transfers.
I have tried with 128 and 144, but the transfer rate is only a little
bit higher barely measurable. Or what values should I try?

> > Version  1.03        ------Sequential Output------ --Sequential Input- --Random-
> >                       -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
> > Machine         Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
> > Raid0 (8 disk)15744M 54406  96 247419 90 100752 25 60266  98 226651 29 830.2   1
> > Raid0s(4 disk)15744M 54915  97 253642 89 73976  18 59445  97 198372 24 659.8   1
> > Raid0s(4 disk)15744M 54866  97 268361 95 72852  17 59165  97 187183 22 666.3   1
>
> you're obviously saturating something already with 2 disks.  did you play
> with "blockdev --setra" setings?
Yes, I did play a little bit with it but this only changed read performance,
it made no measurable difference when writting.

Thanks,
Holger

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/