Messages in this thread | | | From | Namhyung Kim <> | Date | Thu, 29 Oct 2020 20:15:19 +0900 | Subject | Re: [PATCH] perf data: Allow to use stdio functions for pipe mode |
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Hi Ian,
On Thu, Oct 29, 2020 at 1:37 AM Ian Rogers <irogers@google.com> wrote: > > On Wed, Oct 28, 2020 at 1:56 AM Namhyung Kim <namhyung@kernel.org> 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. > > This is great! Reading the numbers below the times are reduced to > 67.9% of their previous, this is a little less than 20ms to 8ms so > perhaps check that number.
The numbers before this patch:
$ ./perf bench internals inject-build-id # Running 'internals/inject-build-id' benchmark: Average build-id injection took: 20.594 msec (+- 0.034 msec) Average time per event: 2.019 usec (+- 0.003 usec) Average memory usage: 8319 KB (+- 0 KB) Average build-id-all injection took: 19.443 msec (+- 0.177 msec) Average time per event: 1.906 usec (+- 0.017 usec) Average memory usage: 7490 KB (+- 0 KB)
> > > $ 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.. > > For perf record there is also the async IO used for writing. I like > that this patch is adding the reading to perf_data. Should the async > IO code live in perf_data rather than record? Should async IO be used > for reading in that case? What would be the policy of using stdio, > not-stdio and async IO?
I'm not sure but using async IO for read is meaningless since we cannot do anything without the data. The reason I added this was that the pipe mode does so many small I/O with syscalls. But perf record will mostly do large I/O so I don't expect big speedup for that.
Thanks Namhyung
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