linux-kernel - Re: [PATCH v1 06/15] perf session: load data directory into tool process memory

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Date:   Wed, 21 Oct 2020 16:01:49 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Andi Kleen <ak@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...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 06/15] perf session: load data directory into tool
 process memory


On 21.10.2020 13:57, Namhyung Kim wrote:
> On Wed, Oct 21, 2020 at 7:25 PM Alexey Budankov
> <alexey.budankov@...ux.intel.com> wrote:
>>
>>
>> On 21.10.2020 9:54, Namhyung Kim wrote:
>>> Hi,
>>>
>>> On Tue, Oct 13, 2020 at 8:30 PM Alexey Budankov
>>> <alexey.budankov@...ux.intel.com> wrote:
>>>> On 12.10.2020 19:49, Alexey Budankov wrote:
>>>>> On 12.10.2020 19:09, Andi Kleen wrote:
>>>>>> On Mon, Oct 12, 2020 at 11:58:58AM +0300, Alexey Budankov wrote:
>>>>>>> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
>>>>>>> index 6afc670fdf0c..0752eec19813 100644
>>>>>>> --- a/tools/perf/util/session.c
>>>>>>> +++ b/tools/perf/util/session.c
>>>>>>> @@ -2212,6 +2212,17 @@ reader__process_events(struct reader *rd, struct perf_session *session,
>>>>>>>             goto more;
>>>>>>>
>>>>>>>  out:
>>>>>>> +   if (rd->unmap_file) {
>>>>>>> +           int i;
>>>>>>> +
>>>>>>> +           for (i = 0; i < NUM_MMAPS; i++) {
>>>>>>> +                   if (mmaps[i]) {
>>>>>>> +                           munmap(mmaps[i], mmap_size);
>>>>>>> +                           mmaps[i] = NULL;
>>>>>>
>>>>>> Okay so where is the mmap? Would make more sense to put that
>>>>>> into the same patch as who adds the mmap. Or is the mmap
>>>>>> code already in the perf source? In that case it should
>>>>>> probably be some common helper with the existing users.
>>>>>
>>>>> That mmap is already in the code. Agree, this part of the patch
>>>>> can be applied prior the whole patch set.
>>>>
>>>> I take it back. Single trace file can't be unmapped yet since it also
>>>> contains not only compressed records but also other records backing
>>>> the data for aggregated analysis.
>>>
>>> Are you talking about the auxtrace?
>>>
>>> I thought everything will be compressed when it's enabled.
>>> But if it's only for the auxtrace, maybe we can unmap them
>>> with checking it as it's not the common case?
>>
>> I am about primary trace file. Together with PERF_RECORD_COMPRESSED
>> records it contains the other records with uncompressed data (MMAP,
>> FORk, COMM etc.) so it is still unsafe to unmap the trace file after
>> loading.
> 
> Oh, I think all the events coming from the kernel share the mmap
> buffer so they will be compressed with SAMPLEs.  Note that
> synthesized events have 0 timestamp which means that they
> are not queued in the ordered events and processed immediately.

Yes, they are and it will work as expected with this patch changes.

> 
> IIUC, here we unmap the original mmap buffer and the actual data
> in MMAP/FORK/... is kept in the decomp data buffer, no?

Correct. It unmaps trace file from memory after COMPRESSED records
are decompressed into separately allocated decomp objects.

Alexei

> 
> Thanks
> Namhyung
>