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 19:57:53 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
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 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.

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

Thanks
Namhyung