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

[Jens Axboe]

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.

-- 
Jens Axboe