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    SubjectRe: [PATCH] perf data: Allow to use stdio functions for pipe mode
    Hi Jiri,

    On Thu, Oct 29, 2020 at 8:57 PM Jiri Olsa <jolsa@redhat.com> wrote:
    >
    > On Wed, Oct 28, 2020 at 05:56:32PM +0900, Namhyung Kim wrote:
    > > When perf data is in a pipe, it reads each event separately using
    > > read(2) syscall. This is a huge performance bottleneck when
    > > processing large data like in perf inject. Also perf inject needs to
    > > use write(2) syscall for the output.
    > >
    > > So convert it to use buffer I/O functions in stdio library for pipe
    > > data. This makes inject-build-id bench time drops from 20ms to 8ms.
    > >
    > > $ perf bench internals inject-build-id
    > > # Running 'internals/inject-build-id' benchmark:
    > > Average build-id injection took: 8.074 msec (+- 0.013 msec)
    > > Average time per event: 0.792 usec (+- 0.001 usec)
    > > Average memory usage: 8328 KB (+- 0 KB)
    > > Average build-id-all injection took: 5.490 msec (+- 0.008 msec)
    > > Average time per event: 0.538 usec (+- 0.001 usec)
    > > Average memory usage: 7563 KB (+- 0 KB)
    > >
    > > This patch enables it just for perf inject when used with pipe (it's a
    > > default behavior). Maybe we could do it for perf record and/or report
    > > later..
    > >
    > > Signed-off-by: Namhyung Kim <namhyung@kernel.org>
    > > ---
    > > tools/perf/builtin-inject.c | 2 ++
    > > tools/perf/util/data.c | 36 +++++++++++++++++++++++++++++++++---
    > > tools/perf/util/data.h | 11 ++++++++++-
    > > tools/perf/util/header.c | 8 ++++----
    > > tools/perf/util/session.c | 7 ++++---
    > > 5 files changed, 53 insertions(+), 11 deletions(-)
    > >
    > > diff --git a/tools/perf/builtin-inject.c b/tools/perf/builtin-inject.c
    > > index 452a75fe68e5..14d6c88fed76 100644
    > > --- a/tools/perf/builtin-inject.c
    > > +++ b/tools/perf/builtin-inject.c
    > > @@ -853,10 +853,12 @@ int cmd_inject(int argc, const char **argv)
    > > .output = {
    > > .path = "-",
    > > .mode = PERF_DATA_MODE_WRITE,
    > > + .use_stdio = true,
    > > },
    > > };
    > > struct perf_data data = {
    > > .mode = PERF_DATA_MODE_READ,
    > > + .use_stdio = true,
    > > };
    > > int ret;
    > >
    > > diff --git a/tools/perf/util/data.c b/tools/perf/util/data.c
    > > index c47aa34fdc0a..47b5a4b50ca5 100644
    > > --- a/tools/perf/util/data.c
    > > +++ b/tools/perf/util/data.c
    > > @@ -174,8 +174,16 @@ static bool check_pipe(struct perf_data *data)
    > > is_pipe = true;
    > > }
    > >
    > > - if (is_pipe)
    > > - data->file.fd = fd;
    > > + if (is_pipe) {
    > > + if (data->use_stdio) {
    > > + const char *mode;
    > > +
    > > + mode = perf_data__is_read(data) ? "r" : "w";
    > > + data->file.fptr = fdopen(fd, mode);
    >
    > I guess fdopen should never fail right? but I think we should
    > add BUG_ON(data->file.fptr == NULL) or something

    The man page says it may fail when mode is invalid or malloc
    failed internally. Will add the check.

    >
    > other than this the change looks good, I can see the speedup
    > in bench as well

    Thanks!
    Namhyung

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