linux-kernel - Re: [PATCH] perf intel-pt: Synthesize cycle events

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Message-ID: <ef780335-7dc6-3a23-54a8-b6fc9c8a2ed3@intel.com>
Date:   Wed, 16 Mar 2022 13:19:46 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     "Steinar H. Gunderson" <sesse@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf intel-pt: Synthesize cycle events

On 16.3.2022 10.19, Steinar H. Gunderson wrote:
> On Tue, Mar 15, 2022 at 10:11:54PM +0200, Adrian Hunter wrote:
>> Sorry, my first suggestion has issues, but the second is better.
> 
> I tried your second one, but can't see much difference. The original and
> your patched version still differ by a lot, and I still see various
> non-branch instructions getting very tiny fractions. (PSB packets
> _might_ be it, as there are ~1000 of them in the 165M-cycle trace.)
> 
> I guess the good news is that the perf report coming out of your version
> looks more likely to me; I have some functions that are around 1% that
> shouldn't intuitively be that much (and, if I write some Perl to sum up
> the cycles from the IPC lines in perf script, are more around 0.1%).
> So perhaps we should stop chasing the difference? I don't know.

That doesn't sound right.  I will look at it more closely in the next few days.