Re: Time sliced CFQ io scheduler

Jens Axboe
2004-12-03T09:44:05Z

On Fri, Dec 03 2004, Prakash K. Cheemplavam wrote:
> Jens Axboe schrieb:
> >On Fri, Dec 03 2004, Prakash K. Cheemplavam wrote:
> >
> >>Jens Axboe schrieb:
> >>
> >>>On Thu, Dec 02 2004, Prakash K. Cheemplavam wrote:
> >>>
> >>
> >>>>0 3 3080 2208 1156 817712 0 0 3592 75624 1326 2289 1 36
> >>>>0 63
> >>>>0 3 3080 2664 1156 818240 0 0 5124 15692 1302 992 1 18
> >>>>0 81
> >>>>0 3 3080 2580 1160 815832 0 0 4356 155792 1375 1064 1
> >>>>39 0 60
> >>>>0 3 3080 2472 1160 817124 0 0 3076 100852 1345 1138 1
> >>>>23 0 76
> >>>>2 4 3080 2836 1148 816228 0 0 3336 100412 1352 1379 1
> >>>>47 0 52
> >>>>0 4 3080 2708 1144 815964 0 0 3844 48908 1343 871 1 25
> >>>>0 74
> >>>>0 3 3080 2748 1152 815984 0 0 3332 71996 1338 843 1 27
> >>>>0 72
> >>>
> >>>
> >>>Can you try with the patch that is in the parent of this thread? The
> >>>above doesn't look that bad, although read performance could be better
> >>>of course. But try with the patch please, I'm sure it should help you
> >>>quite a lot.
> >>>
> >>
> >>It actually got worse: Though the read rate seems accepteble, it is not,
> >>as interactivity is dead while writing. I cannot start porgrammes, other
> >>programmes which want to do i/o pretty much hang. This is only while
> >>writing. While reading there is no such problem.
> >
> >
> >Interesting, thanks for testing. I'll run some tests here as well, so
> >far only the cases mentioned yesterday have been tested.
>
> BTW, in case it is misread: Above (except the io performance as such) is
> no regression: The other schedulers behave the same on my system.

Yes, that's what I assumed. Another thing to keep in mind is that even
with just a single writer, you could have 3 people doing writeout for
you (pdflush for each disk, and the writer itself), while the reader is
on its own. This could affect latencies/bandwidth for the reader in
not-so pleasant ways.

> >You could try and bumb the slice period. But I'll experiment and see
> >what happens. What is your test case?
>
> [slice bumping] Uhm, is it doable via proc? I haven't seen text docs to
> your patch and I am not good at kernel code ;-)

:-)

See my previous mail, it tells you how to do it.

--
Jens Axboe