linux-kernel - Re: [tip:perf/core] perf/x86: Use INST_RETIRED.PREC

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Message-ID: <20151206131102.GA12167@gmail.com>
Date:	Sun, 6 Dec 2015 14:11:02 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	vincent.weaver@...ne.edu, jolsa@...hat.com,
	torvalds@...ux-foundation.org, eranian@...gle.com,
	tglx@...utronix.de, acme@...hat.com, ak@...ux.intel.com,
	peterz@...radead.org, linux-kernel@...r.kernel.org, hpa@...or.com
Cc:	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/core] perf/x86: Use INST_RETIRED.PREC_DIST for cycles:
 ppp


* tip-bot for Andi Kleen <tipbot@...or.com> wrote:

> Commit-ID:  4576ceaa56a86bd0c041c204d51c3f3ca582a49c
> Gitweb:     http://git.kernel.org/tip/4576ceaa56a86bd0c041c204d51c3f3ca582a49c
> Author:     Andi Kleen <ak@...ux.intel.com>
> AuthorDate: Mon, 30 Nov 2015 16:28:09 -0800
> Committer:  Ingo Molnar <mingo@...nel.org>
> CommitDate: Fri, 4 Dec 2015 10:08:04 +0100
> 
> perf/x86: Use INST_RETIRED.PREC_DIST for cycles:ppp
> 
> Add a new 'three-p' precise level, that uses INST_RETIRED.PREC_DIST as
> base. The basic mechanism of abusing the inverse cmask to get all
> cycles works the same as before.

So this commit regressed on the follwing Intel Nehalem box:

 processor       : 15
 vendor_id       : GenuineIntel
 cpu family      : 6
 model           : 26
 model name      : Intel(R) Xeon(R) CPU           X55600 @ 2.80GHz
 stepping        : 5
 cpu MHz         : 2793.000
 cache size      : 8192 KB
 it has this perf bootup signature:

    0.272504] Performance Events: PEBS fmt1+, 16-deep LBR, Nehalem events, Intel PMU driver.
    0.281356] perf_event_intel: CPU erratum AAJ80 worked around

the symptom is that latest 'perf top' and 'perf record' produces no samples.

So I've removed this commit and the related Skylake commit from -tip:

 4576ceaa56a8 perf/x86: Use INST_RETIRED.PREC_DIST for cycles:ppp
 ac1e1d30cf90 perf/x86: Use INST_RETIRED.TOTAL_CYCLES_PS for cycles:pp for Skylake

you need to do better testing next time around. Note: if you resubmit the patches, 
please also pick up the updates commit changelogs from the tip-bot emails, don't 
use your original changelogs.

Also, I'm not convinced we need a new 'ppp' qualifier for any of this, why not 
just replace 'pp' with this event - 'pp' is meant to be our most precise event.

Thanks,

	Ingo
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