linux-kernel - Re: [PATCH v1 08/15] perf record: write trace data into mmap trace files

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Date:   Wed, 21 Oct 2020 16:34:55 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 08/15] perf record: write trace data into mmap trace files

On Wed, Oct 14, 2020 at 9:09 PM Alexey Budankov
<alexey.budankov@...ux.intel.com> wrote:
>
> Hi,
>
> On 14.10.2020 13:52, Namhyung Kim wrote:
> > Hi,
> >
> > On Mon, Oct 12, 2020 at 6:01 PM Alexey Budankov
> > <alexey.budankov@...ux.intel.com> wrote:
> >>
> >>
> >> Write trace data into per mmap trace files located
> >> at data directory. Streaming thread adjusts its affinity
> >> according to mask of the buffer being processed.
> >>
> >> Signed-off-by: Alexey Budankov <alexey.budankov@...ux.intel.com>
> >> ---
> > [SNIP]
> >> @@ -1184,8 +1203,12 @@ static int record__mmap_read_evlist(struct record *rec, struct evlist *evlist,
> >>         /*
> >>          * Mark the round finished in case we wrote
> >>          * at least one event.
> >> +        *
> >> +        * No need for round events in directory mode,
> >> +        * because per-cpu maps and files have data
> >> +        * sorted by kernel.
> >>          */
> >> -       if (bytes_written != rec->bytes_written)
> >> +       if (!record__threads_enabled(rec) && bytes_written != rec->bytes_written)
> >>                 rc = record__write(rec, NULL, &finished_round_event, sizeof(finished_round_event));
> >
> > This means it needs to keep all events in the ordered events queue
> > when perf report processes the data, right?
>
> Looks so.

Maybe it's not related to this directly. But we need to think about
how to make perf report faster and more efficient as well.

In my previous attempt, I separated samples from other events
to be in different mmaps so they were saved to different files
(or in a separate part of the data file).

And perf report processes the meta events (FORK/MMAP/...)
first to construct the system image and then processes samples
with multi-threads.

Once it has the image, it could bypass the ordered events queue
entirely.

Thanks

Namhyung