Re: CFQ v2 high cpu load fix(?)

[Nick Piggin <nickpiggin@yahoo.com.au>]

Ronny V. Vindenes wrote:
> CFQ v2 is much better in a lot of cases, but certain situations trigger
> a cpu load so high it starves the rest of the system thus completely
> ruining the interactive experience. While casually looking at the
> problem, I stumbled upon a patch by Arjan van de Ven sent to lkml on
> sept. 1 (Subject: block fixes). Part of it is already included in the
> CFQ v2 patches and after applying the rest[1] I'm no longer able to
> trigger the problem.
> 
> [1] Patch attached against 2.6.9-rc4-ck1 but applies to rc4-mm1 with
> some minor fuzz.
> 
> 
> 
> ------------------------------------------------------------------------
> 
> --- 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?

The second hunk should be basically a noop.