Re: [PATCH v2] perf bench: add --write-size option to sched pipe

[Breno Leitao <leitao@debian.org>]

hello Namhyung,

On Mon, May 25, 2026 at 09:17:45PM +0000, Namhyung Kim wrote:
> On Thu, May 21, 2026 at 09:15:37AM -0700, Breno Leitao wrote:
> > +		ret = write(td->pipe_write, td->buf, write_size);
> > +		BUG_ON(ret < 0 || (unsigned int)ret != write_size);
> >  		ret = read_pipe(td);
> > -		BUG_ON(ret != sizeof(int));
> > +		BUG_ON(ret < 0 || (unsigned int)ret != write_size);
> 
> Is it possible to return smaller values than required due to signal or
> something?

I tested this on a VM with the patch applied, running the ping-pong with
write_size from 4 B up to 1 MiB, including multi-process and single-CPU
contention runs (millions of iterations). I observed zero short reads or short
writes.

Looking at fs/pipe.c, this matches the kernel behavior for this access pattern:
the bench has a single writer per pipe and the pipe capacity is set to
write_size, so the writer never has to sleep mid-write, and the kernel does a
sync wake of the reader only after the full payload is queued.

EINTR is also not reachable today because the bench installs no signal
handlers and nothing in the call chain delivers signals to the workers

At the same time, I understand the concern and If you'd still prefer defensive
handling (short-return loop + EINTR retry) I can add it in v3 — happy to either
way.

Thanks for the review,
--breno