linux-kernel - Re: perf_event: rdpmc self-monitoring overhead issue

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Date:	Mon, 2 Sep 2013 19:26:59 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Vince Weaver <vincent.weaver@...ne.edu>
Cc:	eranian@...il.com, Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-perf-users@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: perf_event: rdpmc self-monitoring overhead issue

> I assume he means MAP_POPULATE

Yes.

> 
> which does improve things, from ~3000 cycles to ~219 cycles but that's 
> still more overhead than the ~130 or so you get by manually touching the 
> page first.

That seems odd. It should be the same.

Can you do a trace-cmd function trace and compare the two cases?

trace-cmd record -p function_graph ...
trace-cmd report

(as usual for tracing perf remove the useless -pg removal for perf in
kernel/events/Makefile and arch/x86/kernel/cpu/Makefile first)

-Andi
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