linux-kernel - Re: [PATCH] sched: Make schedstats a runtime tunable that is disabled by default

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Message-ID: <20160125112606.GV6357@twins.programming.kicks-ass.net>
Date:	Mon, 25 Jan 2016 12:26:06 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mel Gorman <mgorman@...hsingularity.net>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	Mike Galbraith <mgalbraith@...e.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched: Make schedstats a runtime tunable that is
 disabled by default

On Mon, Jan 25, 2016 at 10:05:31AM +0000, Mel Gorman wrote:
> schedstats is very useful during debugging and performance tuning but it
> incurs overhead. As such, even though it can be disabled at build time,
> it is often enabled as the information is useful.  This patch adds a
> kernel command-line and sysctl tunable to enable or disable schedstats on
> demand. It is disabled by default as someone who knows they need it can
> also learn to enable it when necessary.

So the reason its often enabled in distro configs is (IIRC) that it
enables trace_sched_stat_{wait,sleep,iowait,blocked}().

I've not looked at the details of this patch, but I suspect this patch
would make these tracepoints available but non-functional unless you
poke the magic button.