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Message-ID: <20201026103426.GC2726983@krava>
Date: Mon, 26 Oct 2020 11:34:26 +0100
From: Jiri Olsa <jolsa@...hat.com>
To: Alexei Budankov <budankov.lore@...il.com>
Cc: Alexey Budankov <alexey.budankov@...ux.intel.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Adrian Hunter <adrian.hunter@...el.com>,
Andi Kleen <ak@...ux.intel.com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 12/15] perf record: introduce thread local variable
for trace streaming
On Mon, Oct 26, 2020 at 11:21:28AM +0300, Alexei Budankov wrote:
>
> On 24.10.2020 18:43, Jiri Olsa wrote:
> > On Wed, Oct 21, 2020 at 07:07:00PM +0300, Alexey Budankov wrote:
> >>
> >> Introduce thread local variable and use it for threaded trace streaming.
> >>
> >> Signed-off-by: Alexey Budankov <alexey.budankov@...ux.intel.com>
> >> ---
> >> tools/perf/builtin-record.c | 71 ++++++++++++++++++++++++++++++++-----
> >> 1 file changed, 62 insertions(+), 9 deletions(-)
> >>
> >> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> >> index 89cb8e913fb3..3b7e9026f25b 100644
> >> --- a/tools/perf/builtin-record.c
> >> +++ b/tools/perf/builtin-record.c
> >> @@ -101,6 +101,8 @@ struct thread_data {
> >> u64 bytes_written;
> >> };
> >>
> >> +static __thread struct thread_data *thread;
> >> +
> >> struct record {
> >> struct perf_tool tool;
> >> struct record_opts opts;
> >> @@ -587,7 +589,11 @@ static int record__pushfn(struct mmap *map, void *to, void *bf, size_t size)
> >> }
> >> }
> >>
> >> - rec->samples++;
> >> + if (thread)
> >> + thread->samples++;
> >> + else
> >> + rec->samples++;
> >
> > this is really wrong, let's keep just single samples counter
> > ditto for all the other places in this patch
>
> This does look like data parallelism [1] which is very true for
> threaded trace streaming so your prototype design looks optimal.
>
> For this specific place incrementing global counter in memory is
> less performant and faces scalability limitations as a number of
> cores grow.
>
> Not sure why you have changed your mind.
I'm not sure I follow.. what I'm complaining about is to have
'samples' stat variable in separate locations for --threads
and --no-threads mode
jirka
>
> Alexei
>
> [1] https://en.wikipedia.org/wiki/Data_parallelism#:~:text=Data%20parallelism%20is%20parallelization%20across,on%20each%20element%20in%20parallel.
>
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