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

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Message-ID: <0dd08c91-f48d-28db-92ed-a2b014bdcb05@linux.intel.com>
Date:   Wed, 21 Oct 2020 13:24:51 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Namhyung Kim <namhyung@...nel.org>
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 21.10.2020 10:34, Namhyung Kim wrote:
> 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.

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.

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

Thanks,
Alexei