linux-kernel - Re: Add top down metrics to perf stat v2

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Message-ID: <CABPqkBTP4JpL+tsXtAaXnETVu4iGTti=zw2ZVt90BSfsF+en1Q@mail.gmail.com>
Date:	Thu, 17 Dec 2015 15:31:30 -0800
From:	Stephane Eranian <eranian@...gle.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Jiri Olsa <jolsa@...nel.org>, Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Namhyung Kim <namhyung@...nel.org>
Subject: Re: Add top down metrics to perf stat v2

On Thu, Dec 17, 2015 at 6:01 AM, Andi Kleen <andi@...stfloor.org> wrote:
> On Thu, Dec 17, 2015 at 02:27:58AM -0800, Stephane Eranian wrote:
>> > S0-C1           2      4175583320.00      topdown-slots-retired                                         (100.00%)
>> > S0-C1           2         1743329246      topdown-recovery-bubbles  #    22.22% bad speculation         (100.00%)
>> > S0-C1           2      6138901193.50      topdown-slots-issued      #    46.99% backend bound
>> >
>> I don't see how this output could be very useful. What matters is the
>> percentage in the comments
>> and not so much the raw counts because what is the unit? Same remark
>> holds for the percentage.
>> I think you need to explain or show that this is % of issue slots and
>> not cycles.
>
> The events already say slots, not cycles. Except for recovery-bubbles. Could add
> -slots there too if you think it's helpful, although it would make the
> name very long and may not fit into the column anymore.
>
I would drop the default output, it is not useful.

I would not add a --topdown option but instead a --metric option with arguments
such that other metrics could be added later:

   $ perf stat --metrics topdown -I 1000 -a sleep 100

If you do this, you do not need the --metric-only option

The double --topdown is confusing.

Why force --per-core when HT is on. I know you you need to aggregate
per core, but
you could still display globally. And then if user requests
--per-core, then display per core.
Same if user specifies --per-socket. I know this requires some more
plumbing inside perf
but it would be clearer and simpler to interpret to users.

One bug I found when testing is that if you do with HT-on:

$ perf stat -a --topdown -I 1000 --metric-only sleep 100
Then you get data for frontend and backend but nothing for retiring or
bad speculation.

I suspect it is because you expect --metric-only to be used only when
you have the
double --topdown. That's why I think this double topdown is confusing. If you do
as I suggest, it will be much simpler.

>>
>> >        1.535832673 seconds time elapsed
>> >
>> > $ perf stat --topdown --topdown --metric-only -I 100 ./BC1s
>>
>> When I tried from your git tree the --metric-only option was not recognized.
>
> See below.
>>
>> >      0.100576098 frontend bound           retiring                 bad speculation          backend bound
>> >      0.100576098     8.83%                  48.93%                  35.24%                   7.00%
>> >      0.200800845     8.84%                  48.49%                  35.53%                   7.13%
>> >      0.300905983     8.73%                  48.64%                  35.58%                   7.05%
>> > ...
>> >
>> This kind of output is more meaningful and clearer for end-users based
>> on my experience
>> and you'd like it per-core possibly.
>
> Yes --metric-only is a lot clearer.
>
> per-core is supported and automatically enabled with SMT on.
>
>> > Full tree available in
>> > git://git.kernel.org/pub/scm/linux/kernel/git/ak/linux-misc perf/top-down-11
>>
>> That is in the top-down-2 branch instead, I think.
>
> Sorry, typo
>
> The correct branch is perf/top-down-10
>
> I also updated it now with the latest review feedback changes.
>
> top-down-2 is an really old branch that indeed didn't have metric-only.
>
> -Andi
>
> --
> ak@...ux.intel.com -- Speaking for myself only.
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