linux-kernel - Re: [PATCH 0/26] oprofile: Performance counter multiplexing

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Message-ID: <20100305164615.GY13205@erda.amd.com>
Date:	Fri, 5 Mar 2010 17:46:15 +0100
From:	Robert Richter <robert.richter@....com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Mike Galbraith <efault@....de>,
	LKML <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Paul Mackerras <paulus@...ba.org>,
	oprofile-list <oprofile-list@...ts.sourceforge.net>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 0/26] oprofile: Performance counter multiplexing

On 26.02.10 15:51:04, Andi Kleen wrote:
> That said the biggest problem with oprofile right now that the
> new buffer it's using is quite a lot less reliable and drops
> events left and right on any non trivial load. That makes
> oprofile very unreliable, especially in call graph mode.

(cc'ing Steve)

Andi,

the tests I run with oprofile do not indicate unreliable ring_buffer
behavior. Maybe my use cases and loads are different. Can you describe
a setup where this may happen for sure? What is the impact, do you
have lost samples or inconsistent buffer data? Is the data loss in
kernel or user space? Also, I am not aware that the ring_buffer is
unreliable for ftrace or tracepoints, where it is heavily used. I
really want to find the root cause here.

Thanks,

-Robert

-- 
Advanced Micro Devices, Inc.
Operating System Research Center
email: robert.richter@....com

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