linux-kernel - Re: [tip:timers/urgent] hrtimer: Fix /proc/timer

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Message-ID: <20091120141959.GA6781@osiris.boeblingen.de.ibm.com>
Date:	Fri, 20 Nov 2009 15:19:59 +0100
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, tglx@...utronix.de, feng.tang@...el.com
Cc:	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:timers/urgent] hrtimer: Fix /proc/timer_list regression

On Fri, Nov 20, 2009 at 10:30:39AM +0000, tip-bot for Feng Tang wrote:
> Commit-ID:  8629ea2eaba8ca0de2e38ce1b4a825e16255976e
> Gitweb:     http://git.kernel.org/tip/8629ea2eaba8ca0de2e38ce1b4a825e16255976e
> Author:     Feng Tang <feng.tang@...el.com>
> AuthorDate: Thu, 3 Sep 2009 16:32:53 +0800
> Committer:  Thomas Gleixner <tglx@...utronix.de>
> CommitDate: Fri, 20 Nov 2009 11:25:48 +0100
> 
> hrtimer: Fix /proc/timer_list regression
> 
> commit 507e1231 (timer stats: Optimize by adding quick check to avoid
> function calls) introduced a regression in /proc/timer_list.
> 
> /proc/timer_list shows now
>  #0: <c27d46b0>, tick_sched_timer, S:01, <(null)>, /-1
> instead of
>  #0: <c27d46b0>, tick_sched_timer, S:01, hrtimer_start, swapper/0

For a 'real' fix I see three possible ways if timer_stats are disabled:

Print something like:

#0: <c27d46b0>, tick_sched_timer, S:01, unknown, unknown/-1

That way the format would be still the same and it should be quite obvious
that timer_stats are disabled and should be enabled.

Alternatively leave start_site, taskname and pid away if the correspending
timer has a NULL start_site. That would be the same like for the !TIMER_STATS
case:

#0: <c27d46b0>, tick_sched_timer, S:01

or (worst choice) revert the whole optimization and live with extra cpu cost.
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