linux-kernel - Re: [PATCH] hrtimers: Remove the "timer_stats_active" check when setting the start info

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Date:	Tue, 15 Sep 2009 11:00:09 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Feng Tang <feng.tang@...el.com>
cc:	LKML <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH] hrtimers: Remove the "timer_stats_active" check when
 setting the start info

On Thu, 3 Sep 2009, Feng Tang wrote:
> Please review this patch (generated against v2.6.31-rc8)
> 
> Thanks,
> Feng
> 
> >From 8c6b53a0ead71590a0dd5556c9ad409f0c1ad2d1 Mon Sep 17 00:00:00 2001
> From: Feng Tang <feng.tang@...el.com>
> Date: Thu, 3 Sep 2009 15:51:10 +0800
> Subject: [PATCH] hrtimers: Remove the "timer_stats_active" check when setting the start info
> 
> Recent hrtimer code will set the start info to a hrtimer only when that
> flag is set, then the start info of all hrtimers will always be uninitialised
> before a "echo 1 > /proc/timer_stats", thus the /proc/timer_lists will have
> something like:
> 
> active timers:
>  #0: <c27d46b0>, tick_sched_timer, S:01, <(null)>, /-1
>  # expires at 91062000000-91062000000 nsecs [in 156071 to 156071 nsecs]
>  #1: <efb81b6c>, hrtimer_wakeup, S:01, <(null)>, /-1
>  # expires at 91062300331-91062350331 nsecs [in 456402 to 506402 nsecs]
>  #2: <efac9b6c>, hrtimer_wakeup, S:01, <(null)>, /-1
>  # expires at 91068699811-91068749811 nsecs [in 6855882 to 6905882 nsecs]
>  #3: <efacdb6c>, hrtimer_wakeup, S:01, <(null)>, /-1
>  # expires at 91068755511-91068805511 nsecs [in 6911582 to 6961582 nsecs]
>  #4: <efa95b6c>, hrtimer_wakeup, S:01, <(null)>, /-1
>  # expires at 91068806066-91068856066 nsecs [in 6962137 to 7012137 nsecs]
>  .....
> 
> This patch will fix it.

Well, at the same time it forces the memcpy when !timer_stats_active.
We generally want to avoid such overhead when debug facilities are
disabled.

Thanks,

	tglx
 
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