Re: [git patches] IDE update

Jens Axboe
2005-07-05T19:17:52Z

On Tue, Jul 05 2005, Ondrej Zary wrote:
> Jens Axboe wrote:
> >On Tue, Jul 05 2005, Ondrej Zary wrote:
> >
> >>Jens Axboe wrote:
> >>
> >>>On Tue, 2005-07-05 at 15:02 +0200, Ondrej Zary wrote:
> >>>
> >>>
> >>>>>Ok, looks alright for both. Your machine is quite slow, perhaps that is
> >>>>>showing the slower performance. Can you try and make HZ 100 in 2.6 and
> >>>>>test again? 2.6.13-recent has it as a config option, otherwise edit
> >>>>>include/asm/param.h appropriately.
> >>>>>
> >>>>
> >>>>I forgot to write that my 2.6.12 kernel is already compiled with HZ 100
> >>>>(it makes the system more responsive).
> >>>>I've just tried 2.6.8.1 with HZ 1000 and there is no difference in HDD
> >>>>performance comparing to 2.6.12.
> >>>
> >>>
> >>>OK, interesting. You could try and boot with profile=2 and do
> >>>
> >>># readprofile -r
> >>># dd if=/dev/hda of=/dev/null bs=128k
> >>># readprofile > prof_output
> >>>
> >>>for each kernel and post it here, so we can see if anything sticks out.
> >>>
> >>
> >>Here are the profiles (used dd with count=4096) from 2.4.26 and 2.6.12
> >>(nothing from 2.6.8.1 because I don't have the .map file anymore).
> >
> >
> >Looks interesting, 2.6 spends oodles of times copying to user space.
> >Lets check if raw reads perform ok, please try and time this app in 2.4
> >and 2.6 as well.
> >
> ># gcc -Wall -O2 -o oread oread.c
> ># time ./oread /dev/hda
> >
> oread is faster than dd, but still not as fast as 2.4. In 2.6.12, HDD
> led is blinking, in 2.4 it's solid on during the read.
>
> 2.6.12:
> root@pentium:/home/rainbow# time ./oread /dev/hda
>
> real 0m25.082s
> user 0m0.000s
> sys 0m0.680s
>
> 2.4.26:
> root@pentium:/home/rainbow# time ./oread /dev/hda
>
> real 0m23.513s
> user 0m0.000s
> sys 0m2.360s

Hmm, still not as fast, not so good. 2.6 shows more idle time than 2.4,
about 20% more. I seem to remember Ken Chen saying that 2.6 direct io
was still a little slower than 2.4, your really slow hardware could be
showing this to a much greater effect.

I'll try and play with this tomorrow!

--
Jens Axboe