linux-kernel - Re: [PATCH] sched: do not stop ticks when cpu is not idle

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Message-ID: <20080718105424.GA22268@elte.hu>
Date:	Fri, 18 Jul 2008 12:54:24 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	eric miao <eric.y.miao@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Jack Ren <jack.ren@...vell.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>
Subject: Re: [PATCH] sched: do not stop ticks when cpu is not idle


* Ingo Molnar <mingo@...e.hu> wrote:

> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -4446,7 +4446,8 @@ need_resched_nonpreemptible:
>  		rq->nr_switches++;
>  		rq->curr = next;
>  		++*switch_count;
> -
> +		if (rq->curr != rq->idle)
> +			tick_nohz_restart_sched_tick();
>  		context_switch(rq, prev, next); /* unlocks the rq */

hm, one problem i can see is lock dependencies. This code is executed 
with the rq lock while tick_nohz_restart_sched_tick() takes hr locks => 
not good. So i havent applied this just yet - this needs to be solved 
differently.

	Ingo
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