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

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Date:	Mon, 25 Jan 2016 17:07:16 +0000
From:	Mel Gorman <mgorman@...hsingularity.net>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Peter Zijlstra <peterz@...radead.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 04:46:35PM +0100, Ingo Molnar wrote:
> > Of course, it'll be our luck that tracking the data for these
> > tracepoints is the most expensive part of schedstats ...
> > 
> > Ingo?
> 
> IIRC it needed only a small subset of schedstats to make those tracepoints work.
> 
> We already have too much overhead in the scheduler as-is - and the extra cache 
> footprint does not even show on the typically cache-rich enterprise CPUs most of 
> the scalability testing goes on.
> 
> My minimum requirement for such runtime enablement would be to make it entirely 
> static-branch patched and triggered at the call sites as well - not hidden inside 
> schedstat functions.
> 

As it is, it's static-branch patched but I'm struggling to see why they
cannot be hidden in the schedstat_* functions which are just preprocessor
macros. The checks could be put in the callsites but it's a lot of updates
and I don't think the end result would be very nice to read.

-- 
Mel Gorman
SUSE Labs