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

[Namhyung Kim <namhyung@kernel.org>]

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,
Namhyung