linux-kernel - Re: [PATCH 8/8] watchdog: Remove hack to make full dynticks working

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Message-ID: <20130723123331.GE126784@redhat.com>
Date:	Tue, 23 Jul 2013 08:33:31 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Stephane Eranian <eranian@...gle.com>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Anish Singh <anish198519851985@...il.com>
Subject: Re: [PATCH 8/8] watchdog: Remove hack to make full dynticks working

On Tue, Jul 23, 2013 at 02:31:06AM +0200, Frederic Weisbecker wrote:
> A perf event can be used without forcing the tick to
> stay alive if it doesn't use a frequency but a sample
> period and if it doesn't throttle (raise storm of events).
> 
> Since the lockup detector neither use a perf event frequency
> nor should ever throttle due to its high period, it can now
> run concurrently with the full dynticks feature.

Thanks.  Dumb question, I keep wondering if the lockup detector would be
better or worse off if it used the perf event frequency as opposed to
using a sample period?  The idea is it could follow the varying cpu
frequencies better (and probably simplify some of the code too).

Acked-by: Don Zickus <dzickus@...hat.com>


> 
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Jiri Olsa <jolsa@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Stephane Eranian <eranian@...gle.com>
> Cc: Don Zickus <dzickus@...hat.com>
> Cc: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
> Cc: Anish Singh <anish198519851985@...il.com>
> ---
>  kernel/watchdog.c |    8 --------
>  1 files changed, 0 insertions(+), 8 deletions(-)
> 
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> index 1241d8c..51c4f34 100644
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -553,14 +553,6 @@ void __init lockup_detector_init(void)
>  {
>  	set_sample_period();
>  
> -#ifdef CONFIG_NO_HZ_FULL
> -	if (watchdog_user_enabled) {
> -		watchdog_user_enabled = 0;
> -		pr_warning("Disabled lockup detectors by default for full dynticks\n");
> -		pr_warning("You can reactivate it with 'sysctl -w kernel.watchdog=1'\n");
> -	}
> -#endif
> -
>  	if (watchdog_user_enabled)
>  		watchdog_enable_all_cpus();
>  }
> -- 
> 1.7.5.4
> 
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