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

[Namhyung Kim]

On Wed, Oct 21, 2020 at 7:25 PM Alexey Budankov
<alexey.budankov@xxxxxxxxxxxxxxx> wrote:
>
>
> On 21.10.2020 10:34, Namhyung Kim wrote:
> > On Wed, Oct 14, 2020 at 9:09 PM Alexey Budankov
> > <alexey.budankov@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx>
> >>>> ---
> >>> [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.
>
> Makes sense. Agreed.
>
> >
> > 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.
>
> Looks like separation to global, per-process events and per-thread
> ones. Alternative algorithm could possibly be multi-passing of trace
> data. First pass is to capture global events and build process state
> overtime progress picture. Second pass is to capture and map per-thread
> samples and/or other events into process state according to samples
> and events time.

Yep, it seems basically the same approach.  But it'd be better if
we could do it in a single pass (with some modification in the data
collection).

Thanks
Namhyung