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

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Message-ID: <YjGdoGy4Z2UUG9S9@google.com>
Date:   Wed, 16 Mar 2022 09:19:44 +0100
From:   "Steinar H. Gunderson" <sesse@...gle.com>
To:     Adrian Hunter <adrian.hunter@...el.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 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.

/* Steinar */