Re: sysbench+mysql(oltp, readonly) 30% regression with 2.6.26-rc1

From: Peter Zijlstra
Date: Thu May 08 2008 - 05:24:08 EST


On Thu, 2008-05-08 at 11:15 +0200, Mike Galbraith wrote:
> On Thu, 2008-05-08 at 17:01 +0800, Zhang, Yanmin wrote:
> > On Thu, 2008-05-08 at 10:00 +0200, Mike Galbraith wrote:
>
> > > Hm. I was doing some sysbench+postgress(oltp, ro) testing on my little
> > > Q6600 box this morning, and saw a different picture.
>
> > How many cpu are in the Q6600?
>
> 1.
>
> > >
> > > In attached pdf, .bkl refers to Linus' BKL patch, .weight is the weight
> > > fix, both are applied to git.today. The script I used is also attached.
> > With my 8-core stoakley (using mysql):
> > 1) 2.6.25:
> > Number of threads: 6
> > read/write requests: 8025024 (66874.53 per sec.)
> > Number of threads: 8
> > read/write requests: 9132816 (76106.14 per sec.)
> > Number of threads: 10
> > read/write requests: 9244998 (77040.75 per sec.)
> > Number of threads: 12
> > read/write requests: 8994174 (74950.36 per sec.)
> > Number of threads: 14
> > read/write requests: 9051322 (75426.54 per sec.)
> > Number of threads: 16
> > read/write requests: 9015412 (75126.93 per sec.)
> >
> > 2) 2.6.26-rc1:
> > Number of threads: 6
> > read/write requests: 5754056 (47949.87 per sec.)
> > Number of threads: 8
> > read/write requests: 6528480 (54403.29 per sec.)
> > Number of threads: 10
> > read/write requests: 6444690 (53705.16 per sec.)
> > Number of threads: 12
> > read/write requests: 6544258 (54534.23 per sec.)
> > Number of threads: 14
> > read/write requests: 6796650 (56637.65 per sec.)
> > Number of threads: 16
> > read/write requests: 6718110 (55983.18 per sec.)
> >
> > 3) 2.6.26-rc1+weight
> > ïNumber of threads: 16
> > read/write requests: 3219076 (26824.22 per sec.)
> >
> > I'm not sure if more cpu could introduce more contention in this test.
>
> -rc1. Do you have the fix below applied?

Oooh - good catch, that seems to be a post -rc1 merge.

Yes this is required.

> commit a992241de614dd2b7c97a9ba64e28c0e563f19bf
> Author: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> Date: Mon May 5 23:56:17 2008 +0200
>
> sched: fix normalized sleeper
>
> Normalized sleeper uses calc_delta*() which requires that the rq load is
> already updated, so move account_entity_enqueue() before place_entity()
>
> Tested-by: Frans Pop <elendil@xxxxxxxxx>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
>
> diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
> index 89fa32b..1295ddc 100644
> --- a/kernel/sched_fair.c
> +++ b/kernel/sched_fair.c
> @@ -682,6 +682,7 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int wakeup)
> * Update run-time statistics of the 'current'.
> */
> update_curr(cfs_rq);
> + account_entity_enqueue(cfs_rq, se);
>
> if (wakeup) {
> place_entity(cfs_rq, se, 0);
> @@ -692,7 +693,6 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int wakeup)
> check_spread(cfs_rq, se);
> if (se != cfs_rq->curr)
> __enqueue_entity(cfs_rq, se);
> - account_entity_enqueue(cfs_rq, se);
> }
>
> static void update_avg(u64 *avg, u64 sample)
>
>

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