linux-kernel - Re: [RFC PATCH 0/2] sched: simplify the select_task_rq

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Date:	Mon, 21 Jan 2013 10:09:15 +0100
From:	Mike Galbraith <bitbucket@...ine.de>
To:	Michael Wang <wangyun@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...hat.com,
	peterz@...radead.org, mingo@...nel.org, a.p.zijlstra@...llo.nl
Subject: Re: [RFC PATCH 0/2] sched: simplify the select_task_rq_fair()

On Mon, 2013-01-21 at 15:45 +0800, Michael Wang wrote: 
> On 01/21/2013 03:09 PM, Mike Galbraith wrote:
> > On Mon, 2013-01-21 at 07:42 +0100, Mike Galbraith wrote: 
> >> On Mon, 2013-01-21 at 13:07 +0800, Michael Wang wrote:
> > 
> >>> May be we could try change this back to the old way later, after the aim
> >>> 7 test on my server.
> >>
> >> Yeah, something funny is going on.
> > 
> > Never entering balance path kills the collapse.  Asking wake_affine()
> > wrt the pull as before, but allowing us to continue should no idle cpu
> > be found, still collapsed.  So the source of funny behavior is indeed in
> > balance_path.
> 
> Below patch based on the patch set could help to avoid enter balance path
> if affine_sd could be found, just like the old logical, would you like to
> take a try and see whether it could help fix the collapse?

No, it does not.

> 
> Regards,
> Michael Wang
> 
> ---
>  kernel/sched/fair.c |   14 ++++++++------
>  1 files changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index d600708..4e95bb0 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3297,6 +3297,8 @@ next:
>                         sg = sg->next;
>                 } while (sg != sd->groups);
>         }
> +
> +       return -1;
>  done:
>         return target;
>  }
> @@ -3349,7 +3351,7 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
>                  * some cases.
>                  */
>                 new_cpu = select_idle_sibling(p, prev_cpu);
> -               if (idle_cpu(new_cpu))
> +               if (new_cpu != -1)
>                         goto unlock;
> 
>                 /*
> @@ -3363,15 +3365,15 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
>                         goto balance_path;
> 
>                 new_cpu = select_idle_sibling(p, cpu);
> -               if (!idle_cpu(new_cpu))
> -                       goto balance_path;
> -
>                 /*
>                  * Invoke wake_affine() finally since it is no doubt a
>                  * performance killer.
>                  */
> -               if (wake_affine(sbm->affine_map[prev_cpu], p, sync))
> -                       goto unlock;
> +               if (new_cpu == -1 ||
> +                       !wake_affine(sbm->affine_map[prev_cpu], p, sync))
> +                       new_cpu = prev_cpu;
> +
> +               goto unlock;
>         }
> 
>  balance_path:


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