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b52ba22c70
The default ping-pong uses sizeof(int) (4 bytes) per iteration, which
exercises only the pipe-buffer merge path and keeps allocation entirely
out of the picture. That makes the bench a useful scheduler / context-
switch latency probe but unable to surface anything from the pipe
page-allocation hot path.
Add a -s/--write-size option that sets the bytes written and read per
ping-pong iteration. The buffer is allocated for each side via struct
thread_data and replaces the on-stack int previously used. The default
remains sizeof(int) so existing invocations are unchanged.
With --write-size set above PAGE_SIZE the bench drives anon_pipe_write()
through alloc_page() (or the bulk pre-alloc, if the relevant patch is
applied), which is what we want when measuring pipe locking and page
allocation work.
The bench is a ping-pong: both sides call write() before read(), so a
single write_size payload must fit entirely in the pipe buffer or both
sides deadlock waiting for the other to drain.
Resize the pipe via F_SETPIPE_SZ to match write_size (skipped at the
sizeof(int) default), and error out cleanly when the request exceeds
/proc/sys/fs/pipe-max-size.
Committer testing:
⬢ [acme@toolbx perf-tools-next]$ perf bench sched pipe
# Running 'sched/pipe' benchmark:
# Executed 1000000 pipe operations between two processes
Total time: 0.915 [sec]
0.915493 usecs/op
1092307 ops/sec
⬢ [acme@toolbx perf-tools-next]$ perf bench sched pipe --write-size 1024
# Running 'sched/pipe' benchmark:
# Executed 1000000 pipe operations between two processes
Total time: 0.891 [sec]
0.891915 usecs/op
1121183 ops/sec
⬢ [acme@toolbx perf-tools-next]$ perf bench sched pipe --write-size 4096
# Running 'sched/pipe' benchmark:
# Executed 1000000 pipe operations between two processes
Total time: 1.366 [sec]
1.366073 usecs/op
732025 ops/sec
⬢ [acme@toolbx perf-tools-next]$ strace -e fcntl perf bench sched pipe --write-size 4096
# Running 'sched/pipe' benchmark:
fcntl(4, F_SETPIPE_SZ, 4096) = 4096
fcntl(6, F_SETPIPE_SZ, 4096) = 4096
^Cstrace: Process 17840 detached
⬢ [acme@toolbx perf-tools-next]$ strace -e fcntl perf bench sched pipe --write-size 1024
# Running 'sched/pipe' benchmark:
fcntl(4, F_SETPIPE_SZ, 1024) = 4096
fcntl(6, F_SETPIPE_SZ, 1024) = 4096
^Cstrace: Process 17845 detached
⬢ [acme@toolbx perf-tools-next]$ strace -e fcntl perf bench sched pipe
# Running 'sched/pipe' benchmark:
^Cstrace: Process 17851 detached
⬢ [acme@toolbx perf-tools-next]$
⬢ [acme@toolbx perf-tools-next]$ perf bench sched pipe --write-size 1048577
# Running 'sched/pipe' benchmark:
--write-size 1048577 exceeds /proc/sys/fs/pipe-max-size
⬢ [acme@toolbx perf-tools-next]$ cat /proc/sys/fs/pipe-max-size
1048576
⬢ [acme@toolbx perf-tools-next]$
acme@number:~/git/perf-tools-next$
Signed-off-by: Breno Leitao <leitao@debian.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>