From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: paulmck@linux.vnet.ibm.com
Cc: Jiri Olsa <jolsa@redhat.com>,
linux-kernel@vger.kernel.org,
Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
Ingo Molnar <mingo@elte.hu>, Paul Mackerras <paulus@samba.org>,
Corey Ashford <cjashfor@linux.vnet.ibm.com>,
Frederic Weisbecker <fweisbec@gmail.com>,
Andi Kleen <andi@firstfloor.org>, David Ahern <dsahern@gmail.com>,
Namhyung Kim <namhyung@kernel.org>
Subject: Re: [RFC 00/12] perf diff: Factor diff command
Date: Fri, 07 Sep 2012 09:05:06 +0200 [thread overview]
Message-ID: <1347001506.18408.74.camel@twins> (raw)
In-Reply-To: <20120906212557.GD2448@linux.vnet.ibm.com>
On Thu, 2012-09-06 at 14:25 -0700, Paul E. McKenney wrote:
> On Thu, Sep 06, 2012 at 08:41:09PM +0200, Peter Zijlstra wrote:
> > On Thu, 2012-09-06 at 17:46 +0200, Jiri Olsa wrote:
> > > The 'perf diff' and 'std/hist' code is now changed to allow computations
> > > mentioned in the paper. Two of them are implemented within this patchset:
> > > 1) ratio differential profiling
> > > 2) weighted differential profiling
> >
> > Seems like a useful thing indeed, the explanation of the weighted diff
> > method doesn't seem to contain a why. I know I could go read the paper
> > but... :-)
>
> Or you could ask the author. ;-)
>
> Ratio can be fooled by statistical variations on profiling buckets with
> few counts. So if you are looking for a 10% difference in execution
> overhead somewhere in a large program, ratio will unhelpfully sort a
> bunch of statistical 2x or 3x noise to the top of the list.
>
> So you could use the difference in buckets instead of the ratio, but this
> has problems in the case where the two runs being compared got different
> amounts of work done, as is usually the case for timed benchmark runs
> or throughput-based benchmark runs. In these cases, you use the work
> done (or the measured throughput, as the case may be) as weights.
> The weighted difference will then pinpoint the code that suffered the
> greatest per-unit-work increase in overhead between the two runs.
Ah, ok, I guess that makes sense. Thanks!
prev parent reply other threads:[~2012-09-07 7:05 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-06 15:46 [RFC 00/12] perf diff: Factor diff command Jiri Olsa
2012-09-06 15:46 ` [PATCH 01/12] perf diff: Make diff command work with evsel hists Jiri Olsa
2012-09-08 11:41 ` [tip:perf/core] " tip-bot for Jiri Olsa
2012-09-06 15:46 ` [PATCH 02/12] perf tools: Replace sort's standalone field_sep with symbol_conf.field_sep Jiri Olsa
2012-09-08 11:42 ` [tip:perf/core] perf tools: Replace sort' s " tip-bot for Jiri Olsa
2012-09-06 15:46 ` [PATCH 03/12] perf hists: Add struct hists pointer to struct hist_entry Jiri Olsa
2012-09-06 15:46 ` [PATCH 04/12] perf diff: Refactor diff displacement possition info Jiri Olsa
2012-09-08 0:56 ` Arnaldo Carvalho de Melo
2012-09-06 15:46 ` [PATCH 05/12] perf diff: Refactor stdio ui data columns output Jiri Olsa
2012-09-07 2:55 ` Namhyung Kim
2012-09-07 9:20 ` Jiri Olsa
2012-09-08 12:35 ` Jiri Olsa
2012-09-08 12:50 ` Arnaldo Carvalho de Melo
2012-09-08 14:37 ` Namhyung Kim
2012-09-08 15:10 ` Arnaldo Carvalho de Melo
2012-09-08 15:12 ` Arnaldo Carvalho de Melo
2012-09-08 15:21 ` Arnaldo Carvalho de Melo
2012-09-06 15:47 ` [PATCH 06/12] perf diff: Add -b option for perf diff to display paired entries only Jiri Olsa
2012-09-06 15:47 ` [PATCH 07/12] perf diff: Add ratio computation way to compare hist entries Jiri Olsa
2012-09-07 5:45 ` Namhyung Kim
2012-09-07 9:26 ` Jiri Olsa
2012-09-07 15:33 ` Arnaldo Carvalho de Melo
2012-09-07 15:41 ` Namhyung Kim
2012-09-06 15:47 ` [PATCH 08/12] perf diff: Add option to sort entries based on diff computation Jiri Olsa
2012-09-06 15:47 ` [PATCH 09/12] perf diff: Add weighted diff computation way to compare hist entries Jiri Olsa
2012-09-07 5:58 ` Namhyung Kim
2012-09-07 9:28 ` Jiri Olsa
2012-09-07 13:33 ` Namhyung Kim
2012-09-07 15:26 ` Peter Zijlstra
2012-09-07 15:31 ` Arnaldo Carvalho de Melo
2012-09-07 16:08 ` Peter Zijlstra
2012-09-06 15:47 ` [PATCH 10/12] perf diff: Add -p option to display period values for " Jiri Olsa
2012-09-06 15:47 ` [PATCH 11/12] perf diff: Add -F option to display formula for computation Jiri Olsa
2012-09-07 6:02 ` Namhyung Kim
2012-09-07 9:30 ` Jiri Olsa
2012-09-06 15:47 ` [PATCH 12/12] perf diff: Add -F option for ratio computation Jiri Olsa
2012-09-06 17:31 ` [RFC 00/12] perf diff: Factor diff command Jiri Olsa
2012-09-06 18:41 ` Peter Zijlstra
2012-09-06 21:25 ` Paul E. McKenney
2012-09-07 7:05 ` Peter Zijlstra [this message]
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