Re: elevator=as related to my 2.6 performance issues

[Nick Piggin]

Hi Antti,
Sounds pretty serious. What happens if you set
/sys/block/*/queue/iosched/antic_expire to 0 while
using elevator=as?

Antti Lankila wrote:
> I whined a couple of weeks back with stalling USB and PS/2 mice... I seem to
> have accidentally found a workaround around the issue.
>
> I switched to elevator=deadline the other day and found that it solved my
> issues with stalling USB mice that I'm seeing on 3 computers. Overall the
> system behaves very responsively now during IDE load, none of the bad
> behaviour such as:
>
> - system is something like 80 % idle but still no events from USB or PS/2
>   mice appear in /dev/psaux, thus mouse doesn't move for prolonged periods.
>   I've measured the mouse to stop moving for up to 10 seconds.
>
> - when apt-get dist-upgrade or updatedb is running, games like ut2004 start
>   to stall so much everything gets unplayable. You don't expect
>   /usr/bin/find to cause too much load. On the contrary, you would expect it
>   to be hardly noticeable.
>
> I've seen this on 3 computers now, which have been based on KT266, KT333 and
> Nforce2. Kernels have been 2.6.3-1-k7 (Debian sarge) and 2.6.5 (custom
> compiled).
>
> I tried elevator=deadline because I got tired of the unacceptable
> performance I was seeing from 2.6 and tried to come up with some kind of
> numbers with bonnie++ to prove that 'hey, look there, that's the problem'.
> Bonnie++ numbers with 2.6 AS looked just fine though, CPU usage was down,
> although throughput was not so good as with 2.4 (about 10 % overall
> degradiation in the "intelligent" read and write, but per-char results were
> much better). However, with deadline I got a clear improvement over 2.4 in
> the numbers and the behaviour during bonnie++.
>
> These experiences suggests that I until this get solved I'm going to keep
> anticipatory scheduler off. Either it's directly responsible or just brings
> out some misbehaviour in another place. And yes, I have machines where AS
> never appears to cause any particular kind of trouble, so I got no idea
> what's really wrong. Other people who have had this kind of issues might
> want to try the same trick and report with results.
>
> Antti
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