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Date: Fri, 5 Mar 2010 17:46:15 +0100
From: Robert Richter <robert.richter@amd.com>
To: Andi Kleen <andi@firstfloor.org>
CC: Ingo Molnar <mingo@elte.hu>, Peter Zijlstra <a.p.zijlstra@chello.nl>,
       =?iso-8859-1?Q?Fr=E9d=E9ric?= Weisbecker <fweisbec@gmail.com>,
       Mike Galbraith <efault@gmx.de>, LKML <linux-kernel@vger.kernel.org>,
       Arnaldo Carvalho de Melo <acme@redhat.com>,
       Pekka Enberg <penberg@cs.helsinki.fi>,
       Paul Mackerras <paulus@samba.org>,
       oprofile-list <oprofile-list@lists.sourceforge.net>,
       "H. Peter Anvin" <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Arjan van de Ven <arjan@infradead.org>,
       Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH 0/26] oprofile: Performance counter multiplexing
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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@amd.com