linux-kernel - Re: [RFC] Introduce greedy hrtimer walk on idle

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Message-ID: <m2d3eqkgqj.fsf@firstfloor.org>
Date:	Fri, 23 Sep 2011 15:59:16 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	Venkatesh Pallipadi <venki@...gle.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] Introduce greedy hrtimer walk on idle

Venkatesh Pallipadi <venki@...gle.com> writes:
>
> But, doing an exhaustive search for all softexpired timers, especially when
> CPU is idle, has its advantages:
> * it will result in less interruptions later (when CPU may be busy).
> * it can reduce number of wakeups in cases where not yet expired timer in above description could be deleted before they expire.
> * For timers resulting in task wakeups, doing wakeup on idle can improve the
> overall efficiency of the system. It can also bring load balance/migration benefits.

Seems like a good idea in general.

> diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
> index ca6f7ab..8d3e287 100644
> --- a/arch/x86/kernel/process_64.c
> +++ b/arch/x86/kernel/process_64.c
> @@ -149,6 +149,8 @@ void cpu_idle(void)
>  		preempt_enable_no_resched();
>  		schedule();
>  		preempt_disable();
> +		if (sysctl_hrtimer_greedy_lookup)
> +			hrtimer_peek_ahead_timers();

So why is it a sysctl and not default?

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only
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