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

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Message-ID: <4E7CDE1F.90004@linux.intel.com>
Date:	Fri, 23 Sep 2011 12:29:35 -0700
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Venkatesh Pallipadi <venki@...gle.com>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] Introduce greedy hrtimer walk on idle

On 9/23/2011 11:54 AM, Venkatesh Pallipadi wrote:
> Current hrtimer range timers reduces the number of timer interrupts by
> grouping together softexpired timers until the next unexpired timer.
> It does not look at softexpired timers that may be after the unexpired
> timer in the rbtree.
>
> Specifically, as the comment in hrtimer.c says
> 			 * The immediate goal for using the softexpires is
> 			 * minimizing wakeups, not running timers at the
> 			 * earliest interrupt after their soft expiration.
> 			 * This allows us to avoid using a Priority Search
> 			 * Tree, which can answer a stabbing querry for
> 			 * overlapping intervals and instead use the simple
> 			 * BST we already have.
> 			 * We don't add extra wakeups by delaying timers that
> 			 * are right-of a not yet expired timer, because that
> 			 * timer will have to trigger a wakeup anyway.
>


Since you found that it now makes a difference, I'm all for it..
Acked-by: Arjan van de Ven <arjan@...ux.intel.com>

(at original introduction it was in the noise, but usage patterns 
clearly changed a lot and ranges are much more prevalent now)

I would not do the sysctl/configurability thing though.... that's not 
worth it.

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