Re: [PATCH v4] perf bench: add --write-size option to sched pipe

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Wed, Jun 03, 2026 at 04:34:36PM -0700, Namhyung Kim wrote:
> On Wed, Jun 03, 2026 at 03:35:07AM -0700, Breno Leitao wrote:
> > 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.

> > Signed-off-by: Breno Leitao <leitao@debian.org>

> Acked-by: Namhyung Kim <namhyung@kernel.org>

Thanks, tested and applied:

    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$


- Arnaldo