Re: CFQ v2 high cpu load fix(?)

Nick Piggin
2004-10-12T11:32:39Z

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.