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SubjectRe: [PATCH v1 08/15] perf record: write trace data into mmap trace files
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On 21.10.2020 10:34, Namhyung Kim wrote:
> On Wed, Oct 14, 2020 at 9:09 PM Alexey Budankov
> <alexey.budankov@linux.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@linux.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@linux.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

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