linux-kernel - Re: [PATCH 1/2] sched/nohz: add sysctl control over sched_tick_max

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Date:	Wed, 19 Jun 2013 13:34:23 -0700
From:	Kevin Hilman <khilman@...aro.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	linaro-kernel@...ts.linaro.org, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Clark Williams <clark.williams@...il.com>,
	Tony Luck <tony.luck@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] sched/nohz: add sysctl control over sched_tick_max_deferment

Frederic Weisbecker <fweisbec@...il.com> writes:

> On Tue, Jun 18, 2013 at 04:58:28PM -0700, Kevin Hilman wrote:
>> Allow sysctl override of sched_tick_max_deferment in order to ease
>> finding/fixing the remaining issues with full nohz.
>> 
>> The value to be written is in jiffies, and -1 means the max deferment
>> is disabled (scheduler_tick_max_deferment() returns KTIME_MAX.)
>> 
>> Cc: Frederic Weisbecker <fweisbec@...il.com>
>> Signed-off-by: Kevin Hilman <khilman@...aro.org>
>
> This looks like a useful thing but I wonder if a debugfs file would
> be more appropriate than sysctl.
>
> The scheduler tick max deferment is supposed to be a temporary
> hack so we probably don't want to bring a real user ABI for that.

I wondered about that as well, but I wasn't sure if the existing knobs
under CONFIG_SCHED_DEBUG (sched_min_granularity_ns, sched_latency_ns,
etc.) are considered permanant ABI, or optional debugging tools.

This new option is inside CONFIG_SCHED_DEBUG along with the others, but
if debugfs is preferred I can move it there.  It seems strange though to
just have this knob in debugfs and the rest in sysctl under
CONFIG_SCHED_DEBUG.

Thanks,

Kevin


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