linux-kernel - Re: [PATCH] perf events: Add stalled cycles generic event

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Message-ID: <BANLkTiko3bTCYP9oiX8KuQHQO0j2KtZ-mA@mail.gmail.com>
Date:	Wed, 27 Apr 2011 12:03:12 -0700
From:	Arun Sharma <arun@...rma-home.net>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Arun Sharma <asharma@...com>,
	Stephane Eranian <eranian@...gle.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Lin Ming <ming.m.lin@...el.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, eranian@...il.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] perf events: Add stalled cycles generic event - PERF_COUNT_HW_STALLED_CYCLES

On Wed, Apr 27, 2011 at 8:48 AM, Ingo Molnar <mingo@...e.hu> wrote:

>
>> The other issue I had to deal with was UOPS_RETIRED > UOPS_EXECUTED
>> condition. I believe this is caused by what AMD calls sideband stack
>> optimizer and Intel calls dedicated stack manager (i.e. UOPS executed outside
>> the main pipeline). A recursive fibonacci(30) is a good test case for
>> reproducing this.
>
> So the PORT015+234 sum is not precise? The definition seems to be rather firm:
>
>  Counts number of Uops executed that where issued on port 2, 3, or 4.
>  Counts number of Uops executed that where issued on port 0, 1, or 5.
>

There is some work done outside of the main out of order engine for
power optimization reasons:

Described as dedicated stack engine here:
http://www.intel.com/technology/itj/2003/volume07issue02/art03_pentiumm/vol7iss2_art03.pdf

However, I can't seem to be able to reproduce this behavior using a
micro benchmark right now:

# cat foo.s
.text
        .global main
main:
1:
        push %rax
        push %rbx
        push %rcx
        push %rdx
        pop  %rax
        pop  %rbx
        pop  %rcx
        pop  %rdx
        jmp  1b

 Performance counter stats for './foo':

     7,755,881,073 UOPS_ISSUED:ANY:t=1       (scaled from 79.98%)
    10,569,957,988 UOPS_RETIRED:ANY:t=1      (scaled from 79.96%)
     9,155,400,383 UOPS_EXECUTED:PORT234_CORE  (scaled from 80.02%)
     2,594,206,312 UOPS_EXECUTED:PORT015:t=1  (scaled from 80.02%)

Perhaps I was thinking of UOPS_ISSUED < UOPS_RETIRED.

In general, UOPS_RETIRED (or instruction retirement in general) is the
"source of truth" in an otherwise crazy world and might be more
interesting as a generalized event that works on multiple
architectures.

 -Arun
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