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From: Ingo Molnar <mingo@elte.hu>
To: Dehao Chen <danielcdh@gmail.com>
Cc: Andi Kleen <ak@linux.intel.com>,
	Peter Zijlstra <peterz@infradead.org>,
	arun@sharma-home.net, Stephane Eranian <eranian@google.com>,
	Arnaldo Carvalho de Melo <acme@infradead.org>,
	linux-kernel@vger.kernel.org, Lin Ming <ming.m.lin@intel.com>,
	Arnaldo Carvalho de Melo <acme@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	eranian@gmail.com, Arun Sharma <asharma@fb.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [generalized cache events] Re: [PATCH 1/1] perf tools: Add missing user space support for config1/config2
Date: Mon, 25 Apr 2011 20:05:28 +0200	[thread overview]
Message-ID: <20110425180528.GA30724@elte.hu> (raw)
In-Reply-To: <BANLkTiks31-pMJe4zCKrppsrA1d6KanJFA@mail.gmail.com>


* Dehao Chen <danielcdh@gmail.com> wrote:

> > ... and the resulting low level of noise in the average period length is 
> > what matters. The instruction itself will still be one of the hotspot 
> > instructions, statistically.
> 
> Not true. This skid will lead to some aggregation and shadow effects on some 
> certain instructions. To make things worse, these effects are deterministic 
> and cannot be removed by either sampling for multiple times or by averaging 
> among instructions within a basic block. As a result, some actual "hot spot" 
> are not sampled at all. You can simply try to collect a basic block level 
> CPI, and you'll get a very misleading profile.

This certainly does not match the results i'm seeing on real applications, 
using "-e instructions:pp" PEBS+LBR profiling. How do you explain that? Also, 
can you demonstrate your claim with a real example?

Thanks,

	Ingo

  parent reply	other threads:[~2011-04-25 18:05 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-04-22  8:47 [PATCH 1/1] perf tools: Add missing user space support for config1/config2 Stephane Eranian
2011-04-22  9:23 ` Ingo Molnar
2011-04-22  9:41   ` Stephane Eranian
2011-04-22 10:52     ` [generalized cache events] " Ingo Molnar
2011-04-22 12:04       ` Stephane Eranian
2011-04-22 13:18         ` Ingo Molnar
2011-04-22 20:31           ` Stephane Eranian
2011-04-22 20:47             ` Ingo Molnar
2011-04-23 12:13               ` Stephane Eranian
2011-04-23 12:49                 ` Ingo Molnar
2011-04-22 21:03             ` Ingo Molnar
2011-04-23 12:27               ` Stephane Eranian
2011-04-22 16:51         ` Andi Kleen
2011-04-22 19:57           ` Ingo Molnar
2011-04-26  9:25           ` Peter Zijlstra
2011-04-22 16:50       ` arun
2011-04-22 17:00         ` Andi Kleen
2011-04-22 20:30         ` Ingo Molnar
2011-04-22 20:32           ` Ingo Molnar
2011-04-23  0:03             ` Andi Kleen
2011-04-23  7:50               ` Peter Zijlstra
2011-04-23 12:06                 ` Stephane Eranian
2011-04-23 12:36                   ` Ingo Molnar
2011-04-23 13:16                   ` Peter Zijlstra
2011-04-25 18:48                     ` Stephane Eranian
2011-04-25 19:40                     ` Andi Kleen
2011-04-25 19:55                       ` Ingo Molnar
2011-04-24  2:15                   ` Andi Kleen
2011-04-24  2:19                 ` Andi Kleen
2011-04-25 17:41                   ` Ingo Molnar
2011-04-25 18:00                     ` Dehao Chen
     [not found]                     ` <BANLkTiks31-pMJe4zCKrppsrA1d6KanJFA@mail.gmail.com>
2011-04-25 18:05                       ` Ingo Molnar [this message]
2011-04-25 18:39                         ` Stephane Eranian
2011-04-25 19:45                           ` Ingo Molnar
2011-04-23  8:02               ` Ingo Molnar
2011-04-23 20:14           ` [PATCH] perf events: Add stalled cycles generic event - PERF_COUNT_HW_STALLED_CYCLES Ingo Molnar
2011-04-24  6:16             ` Arun Sharma
2011-04-25 17:37               ` Ingo Molnar
2011-04-26  9:25               ` Peter Zijlstra
2011-04-26 14:00               ` Ingo Molnar
2011-04-27 11:11               ` Ingo Molnar
2011-04-27 14:47                 ` Arun Sharma
2011-04-27 15:48                   ` Ingo Molnar
2011-04-27 16:27                     ` Ingo Molnar
2011-04-27 19:05                       ` Arun Sharma
2011-04-27 19:03                     ` Arun Sharma

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