Re: [patch] 2.5.2 scheduler code for 2.4.18-pre1 ( was 2.5.2-preperformance degradation on an old 486 )

[Davide Libenzi <davidel _at_ xmailserver.org>]

On Mon, 7 Jan 2002, Jens Axboe wrote:

> On Sun, Jan 06 2002, Davide Libenzi wrote:
> > > Davide,
> > >
> > > If this is caused by ISA bounce problems, then you should be able to
> > > reproduce by doing something ala
> > >
> > > [ drivers/ide/ide-dma.c ]
> > >
> > > ide_toggle_bounce()
> > > {
> > > 	...
> > >
> > > +	addr = BLK_BOUNCE_ISA;
> > > 	blk_queue_bounce_limit(&drive->queue, addr);
> > > }
> > >
> > > pseudo-diff, just add the addr = line. Now compare performance with and
> > > without your scheduler changes.
> >
> > I fail to understand where the scheduler code can influence this.
> > There's basically nothing inside blk_queue_bounce_limit()
>
> Eh of course not, no time will be spent inside blk_queue_bounce_limit. I
> don't think you looked very long at this :-)
>
> The point is that ISA bouncing will spend some time scheduling waiting
> for available memory in the __GFP_DMA zone.

I looked and i already pointed out this to Linus.
The memory pool creation ends up by calling alloc_pages and there could
exist race.
I've not had the time for expariments.



- Davide


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