Re: [PATCH linux-next] perf/ring_buffer: Add EPOLLRDNORM flag for poll

[Tao Chen]

在 2025/3/13 18:05, Ingo Molnar 写道:
> * Tao Chen <chen.dylane@xxxxxxxxx> wrote:
>
> > The poll man page says POLLRDNORM is equivalent to POLLIN,
> > so add EPOLLRDNORM here.
> >
> > Signed-off-by: Tao Chen <chen.dylane@xxxxxxxxx>
> > ---
> >   kernel/events/ring_buffer.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
> > index 59a52b1a1..5130b119d 100644
> > --- a/kernel/events/ring_buffer.c
> > +++ b/kernel/events/ring_buffer.c
> > @@ -19,7 +19,7 @@
> >   
> >   static void perf_output_wakeup(struct perf_output_handle *handle)
> >   {
> > -	atomic_set(&handle->rb->poll, EPOLLIN);
> > +	atomic_set(&handle->rb->poll, EPOLLIN | EPOLLRDNORM);
>
> So what does EPOLLRDNORM mean to begin with? There doesn't seem to be
> separate/specific handling of it anywhere in the kernel that I can
> see...

It seems that if user set pollfd with POLLRDNORM, perf_poll will not 
return until timeout even if perf_output_wakeup called, whereas POLLIN 
returns.

> Thanks,
>
> 	Ingo


--
Best Regards
Tao Chen