linux-kernel - Re: [PATCH] clockevents: avoid unnecessary reprograming of event timer

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Date:	Fri, 13 Feb 2009 09:22:23 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Michael Davidson <md@...gle.com>
Cc:	mbligh@...gle.com, tglx@...utronix.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clockevents: avoid unnecessary reprograming of event
	timer


* Michael Davidson <md@...gle.com> wrote:

> From: Michael Davidson <md@...gle.com>
> 
> Don't reprogram the event timer if it is already set to expire
> at the correct time.
> 
> Signed-off-by: Michael Davidson <md@...gle.com>
> ---
> --- linux-2.6.29-rc4.orig/kernel/time/clockevents.c	2009-02-12 13:13:24.000000000 -0800
> +++ linux-2.6.29-rc4/kernel/time/clockevents.c	2009-02-12 13:25:42.525558000 -0800
> @@ -103,6 +103,9 @@
>  	if (delta <= 0)
>  		return -ETIME;
>  
> +	if (ktime_equal(dev->next_event, expires))
> +		return 0;
> +

Hm, given that a good high-res source has nanoseconds resolution,
what's the chance of this optimization triggering in practice?
Near zero i think - unless we trigger useless reprogramming without
having added or removed any new timers - but then we should
concentrate on analyzing the reason for that redundant reprogramming.

Does it trigger often for you?

	Ingo
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