* David Ahern <dsah...@gmail.com> wrote:
> When recording raw_syscalls for the entire system, e.g.,
> perf record -e raw_syscalls:*,sched:sched_switch -a -- sleep 1
>
> you end up with a negative feedback loop as perf itself calls write() fairly
> often. This patch handles the problem by mmap'ing the file in chunks of 64M at
> a time and copies events from the event buffers to the file avoiding write
> system calls.
>
> Before (with write syscall):
>
> perf record -o /tmp/perf.data -e raw_syscalls:*,sched:sched_switch -a --
> sleep 1
> [ perf record: Woken up 0 times to write data ]
> [ perf record: Captured and wrote 81.843 MB /tmp/perf.data (~3575786
> samples) ]
>
> After (using mmap):
>
> perf record -o /tmp/perf.data -e raw_syscalls:*,sched:sched_switch -a --
> sleep 1
> [ perf record: Woken up 31 times to write data ]
> [ perf record: Captured and wrote 8.203 MB /tmp/perf.data (~358388
> samples) ]
>
> In addition to perf-trace benefits using mmap lowers the overhead of
> perf-record. For example,
>
> perf stat -i -- perf record -g -o /tmp/perf.data openssl speed aes
>
> shows a drop in time, CPU cycles, and instructions all drop by more than a
> factor of 3. Jiri also ran a test that showed a big improvement.
>
> v4: Refactoring per Ingo's comments
>
> v3: Removed use of bytes_at_mmap_start at the stat() that set it
> Added user option to control the size of the mmap for writing file.
>
> v2: Removed msync call before munmap per Jiri's suggestion
>
> Signed-off-by: David Ahern <dsah...@gmail.com>
> Cc: Ingo Molnar <mi...@kernel.org>
> Cc: Frederic Weisbecker <fweis...@gmail.com>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Cc: Jiri Olsa <jo...@redhat.com>
> Cc: Namhyung Kim <namhy...@kernel.org>
> Cc: Mike Galbraith <efa...@gmx.de>
> Cc: Stephane Eranian <eran...@google.com>
> ---
> tools/perf/Documentation/perf-record.txt | 5 +
> tools/perf/builtin-record.c | 155
> +++++++++++++++++++++++++++++++
> 2 files changed, 160 insertions(+)
Looks very clean now!
Acked-by: Ingo Molnar <mi...@kernel.org>
Thanks,
Ingo
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