Re: gdth / SCSI read performance issues (2.2.19 and 2.4.10)

Marinos J. Yannikos (mjy@geizhals.at)
Wed, 24 Oct 2001 22:51:02 +0200


Andrew Morton wrote:

> Well that's pretty bad, isn't it?

We could have bought a much cheaper controller and slower disks ;-)

> - Disable CONFIG_HIGHMEM

That seems to have no effect on performance. Btw., the 64GB support in
2.4.10 seemed to be buggy ("0-order allocation failed", then the DB
crashed), so we were using the 4GB setting.

> - Try linux-2.4.13

This helped - now performance is up to par with 2.2.19 (~ 85MB/s) - thanks!

> - Profile the kernel. [...] With something like:
> ~/kern-prof.sh cp some_huge_file /dev/null

I tried this, but with
dd if=/dev/sda of=/dev/null bs=1024k count=3000

(the fs is too slow - so "cp" peaks out at 17MB/s!)

The result (last 4 lines):
c01388fc try_to_free_buffers 55 0.1511
c0128b10 file_read_actor 1179 14.0357
c01053b0 default_idle 6784 130.4615
00000000 total 8695 0.0065

Does this suggest that the kernel isn't the bottleneck?

Regards,
Marinos

-- 
Marinos Yannikos, CEO
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