linux-kernel - Re: [PATCH 2/2] sched: use the old min_vruntime when normalizing on dequeue

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Date:	Thu, 7 Oct 2010 14:00:09 -0700
From:	Dima Zavin <dima@...roid.com>
To:	linux-kernel@...r.kernel.org
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, Mike Galbraith <efault@....de>,
	Dima Zavin <dima@...roid.com>,
	Arve Hjønnevåg <arve@...roid.com>
Subject: Re: [PATCH 2/2] sched: use the old min_vruntime when normalizing on dequeue

Mike,

Thanks for the Ack for patch 1/2, could you take a look at this one too?

Should I re-upload the series as v2 or you can pick the latest from
patch 1 and take this one?

--Dima

On Tue, Sep 28, 2010 at 11:46 PM, Dima Zavin <dima@...roid.com> wrote:
> After pulling the thread off the run-queue during a cgroup change,
> the cfs_rq.min_vruntime gets recalculated. The dequeued thread's vruntime
> then gets normalized to this new value. This can then lead to the thread
> getting an unfair boost in the new group if the vruntime of the next
> task in the old run-queue was way further ahead.
>
> Cc: Arve Hjønnevåg <arve@...roid.com>
> Signed-off-by: Dima Zavin <dima@...roid.com>
> ---
>  kernel/sched_fair.c |    6 +++++-
>  1 files changed, 5 insertions(+), 1 deletions(-)
>
> diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
> index 008fe57..cb24ddb 100644
> --- a/kernel/sched_fair.c
> +++ b/kernel/sched_fair.c
> @@ -802,6 +802,8 @@ static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se)
>  static void
>  dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
>  {
> +       u64 min_vruntime;
> +
>        /*
>         * Update run-time statistics of the 'current'.
>         */
> @@ -826,6 +828,8 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
>        if (se != cfs_rq->curr)
>                __dequeue_entity(cfs_rq, se);
>        account_entity_dequeue(cfs_rq, se);
> +
> +       min_vruntime = cfs_rq->min_vruntime;
>        update_min_vruntime(cfs_rq);
>
>        /*
> @@ -834,7 +838,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
>         * movement in our normalized position.
>         */
>        if (!(flags & DEQUEUE_SLEEP))
> -               se->vruntime -= cfs_rq->min_vruntime;
> +               se->vruntime -= min_vruntime;
>  }
>
>  /*
> --
> 1.6.6
>
>
--
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