Re: CFQ v2 high cpu load fix(?)

[Prakash K. Cheemplavam]

Nick Piggin schrieb:
> Jens Axboe wrote:
>
> > On Tue, Oct 12 2004, Nick Piggin wrote:
> >
> > > Ronny V. Vindenes wrote:
> > >
> > > > --- patches/linux-2.6.9-rc4-ck1/drivers/block/ll_rw_blk.c    
> > > > 2004-10-12 12:25:09.798003278 +0200
> > > > +++ linux-2.6.9-rc4-ck1/drivers/block/ll_rw_blk.c    2004-10-12 
> > > > 12:25:42.959479479 +0200
> > > > @@ -100,7 +100,7 @@
> > > >         nr = q->nr_requests;
> > > >     q->nr_congestion_on = nr;
> > > >
> > > > -    nr = q->nr_requests - (q->nr_requests / 8) - 1;
> > > > +    nr = q->nr_requests - (q->nr_requests / 8) - 
> > > > (q->nr_requests/16)- 1;
> > > >     if (nr < 1)
> > > >         nr = 1;
> > > >     q->nr_congestion_off = nr;
> > >
> > >
> > >
> > > I thought this first hunk looked like a good idea when Arjan sent the
> > > patch. Can you check if it alone helps your problem?
> >
> >
> >
> > Yeah agree, it's a good idea to leave a bit of air between congestion on
> > and off. Fully explains the cfq v2 excessive sys time for some
> > workloads, which is extra nice.
>
> Cool. Can you queue up a patch for when -mm opens again, or shall I?
> I can't imagine it should cause any problems but a bit of testing
> would be wise.

Just as a feedback: I applied the first hunk of that patch to 
2.6.9-rc4-ck1 and it really makes a difference. At first I thought the 
staircase scheduler was responsible for io starvation sometimes, but now 
this behaviour is gone. Very well!

Prakash

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