On Tue, 2006-03-14 at 10:05 +0100, Mike Galbraith wrote:
> On Tue, 2006-03-14 at 08:29 +0100, Ingo Molnar wrote:
> > * Willy Tarreau <[email protected]> wrote:
> >
> > > scheduler is still a big problem. Not only we occasionally see people
> > > complaining about unfair CPU distribution across processes (may be
> > > fixed now), but the scheduler still gives a huge boost to I/O
> > > intensive tasks which do lots of select() with small time-outs, which
> > > makes it practically unusable in network-intensive environments. I've
> > > observed systems on which it was nearly impossible to log in via SSH
> > > because of this, and I could reproduce the problem locally to create a
> > > local DoS where a single user could prevent anybody from logging in.
> > > 2.6.15 has improved a lot on this (pauses have reduced from 35 seconds
> > > to 4 seconds) but it's still not very good.
>
> Hi Willy,
>
> BTW, if you try my stuff, it'd be good to try just the "cleanup" patch
> first. It seems very likely to me that your problem is mostly caused by
> the sleep_avg multiplier. If the first patch cures your woes, try
> killing just the multiplier in virgin source.
Hi again Willy,
Well. I've done some testing with apache, and I can reproduce the
problem... too darn well in fact. It's really bad in 2.6.15 here as
well, and while removing the sleep_avg multiplier and the requeue in
schedule() improved things quite a bit, I still have nasty 30s delays
while trying to pipe commands. These things alone apparently aren't
going to be enough if you want to ssh into a busy server.
-Mike
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