linux-kernel - Re: [patch] BFS 421: remove global runqueue lock in running tick

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Message-ID: <CANQmPXhJEDwO97RBRb-XC+s_FMF6WSJjajj9CO4+wr8UqL5=Rg@mail.gmail.com>
Date:	Fri, 8 Jun 2012 21:45:43 +0800
From:	Chen <hi3766691@...il.com>
To:	unlisted-recipients:; (no To-header on input)
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [patch] BFS 421: remove global runqueue lock in running tick

Still, you haven't produced any usable patch. LOL

On Fri, Jun 8, 2012 at 9:37 PM, Hillf Danton <dhillf@...il.com> wrote:
> We simply deschedule current, with no bother grabbing global lock, since IPI,
> if triggered by preempt, could not change our result, like no schedule when
> preempt enabled.
>
>        preempt_enable_no_resched();
>        if (unlikely(need_resched()))
>                goto need_resched;
>
>
> --- a/kernel/sched/bfs.c        Wed Jun  6 21:02:50 2012
> +++ b/kernel/sched/bfs.c        Fri Jun  8 21:17:24 2012
> @@ -2784,11 +2784,13 @@ static void task_running_tick(struct rq
>        } else if (rq->rq_time_slice >= RESCHED_US)
>                        return;
>
> -       /* p->time_slice < RESCHED_US. We only modify task_struct under grq lock */
> +       /*
> +        * With irq disabled, current is descheduled without global lock
> +        * held and IPI cared.
> +        */
>        p = rq->curr;
> -       grq_lock();
> -       set_tsk_need_resched(p);
> -       grq_unlock();
> +       if (!test_tsk_need_resched(p))
> +               set_tsk_need_resched(p);
>  }
>
>
> --
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