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

[Andrew Morton]

Marinos Yannikos wrote:
> 
> Hi,
> 
> our brand-new ICP GDT8523RZ controller with 6 disks peaks out at
> 45MB/s under 2.4.10, while with 2.2.19 it reaches 85MB/s (seq.
> read performance). It should realistically be able to reach
> at least 150-200MB/s in this configuration

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

Some things which it would be interesting to try out:

- Disable CONFIG_HIGHMEM in your kernel config, see
  what that does.

- Try linux-2.4.13 -- 2.4.10 was a bit of a dog (this may make
  a difference if the driver uese the new PCI DMA API,
  but it doesn't explain why 2.2.x does so much better).

- Profile the kernel.  You may enable profiling by booting
  the kernel with the LILO option `profile=1'.

  Then, making sure that /boot/System.map reflects the
  running kernel, run this little script

#!/bin/sh
TIMEFILE=/tmp/$(basename $1).time
sudo readprofile -r
time "$@"
readprofile -v -m /boot/System.map | sort -n +2 | tail -40 | tee $TIMEFILE
echo created $TIMEFILE

  With something like:

	~/kern-prof.sh cp some_huge_file /dev/null