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

Tao Chen posted 1 patch 9 months, 1 week ago
There is a newer version of this series
kernel/events/ring_buffer.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
[PATCH linux-next] perf/ring_buffer: Add EPOLLRDNORM flag for poll
Posted by Tao Chen 9 months, 1 week ago 
The poll man page says POLLRDNORM is equivalent to POLLIN,
so add EPOLLRDNORM here.

Signed-off-by: Tao Chen <chen.dylane@linux.dev>
---
 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);
 
 	handle->event->pending_wakeup = 1;
 
-- 
2.43.0
Re: [PATCH linux-next] perf/ring_buffer: Add EPOLLRDNORM flag for poll
Posted by Ingo Molnar 9 months, 1 week ago 
* Tao Chen <chen.dylane@linux.dev> wrote:

> The poll man page says POLLRDNORM is equivalent to POLLIN,
> so add EPOLLRDNORM here.
> 
> Signed-off-by: Tao Chen <chen.dylane@linux.dev>
> ---
>  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...

Thanks,

	Ingo
Re: [PATCH linux-next] perf/ring_buffer: Add EPOLLRDNORM flag for poll
Posted by Tao Chen 9 months, 1 week ago 
在 2025/3/13 18:05, Ingo Molnar 写道:
> 
> * Tao Chen <chen.dylane@linux.dev> wrote:
> 
>> The poll man page says POLLRDNORM is equivalent to POLLIN,
>> so add EPOLLRDNORM here.
>>
>> Signed-off-by: Tao Chen <chen.dylane@linux.dev>
>> ---
>>   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
Re: [PATCH linux-next] perf/ring_buffer: Add EPOLLRDNORM flag for poll
Posted by Ingo Molnar 9 months, 1 week ago 
* Tao Chen <chen.dylane@linux.dev> wrote:

> 在 2025/3/13 18:05, Ingo Molnar 写道:
> > 
> > * Tao Chen <chen.dylane@linux.dev> wrote:
> > 
> > > The poll man page says POLLRDNORM is equivalent to POLLIN,
> > > so add EPOLLRDNORM here.
> > > 
> > > Signed-off-by: Tao Chen <chen.dylane@linux.dev>
> > > ---
> > >   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.

Mind adding this to the changelog, and explain that this patch fixes 
this particular poll() functionality and semantics for userspace?

Thanks,

	Ingo
Re: [PATCH linux-next] perf/ring_buffer: Add EPOLLRDNORM flag for poll
Posted by Namhyung Kim 9 months, 1 week ago 
Hello,

On Thu, Mar 13, 2025 at 06:09:45PM +0100, Ingo Molnar wrote:
> 
> * Tao Chen <chen.dylane@linux.dev> wrote:
> 
> > 在 2025/3/13 18:05, Ingo Molnar 写道:
> > > 
> > > * Tao Chen <chen.dylane@linux.dev> wrote:
> > > 
> > > > The poll man page says POLLRDNORM is equivalent to POLLIN,
> > > > so add EPOLLRDNORM here.
> > > > 
> > > > Signed-off-by: Tao Chen <chen.dylane@linux.dev>
> > > > ---
> > > >   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.
> 
> Mind adding this to the changelog, and explain that this patch fixes 
> this particular poll() functionality and semantics for userspace?

Off topic, but I think it should return something (either POLLHUP or
POLLERR) when the event goes to an error state like pinned events are
not scheduled.

Thanks,
Namhyung
Re: [PATCH linux-next] perf/ring_buffer: Add EPOLLRDNORM flag for poll
Posted by Ingo Molnar 9 months, 1 week ago 
* Namhyung Kim <namhyung@kernel.org> wrote:

> Hello,
> 
> On Thu, Mar 13, 2025 at 06:09:45PM +0100, Ingo Molnar wrote:
> > 
> > * Tao Chen <chen.dylane@linux.dev> wrote:
> > 
> > > 在 2025/3/13 18:05, Ingo Molnar 写道:
> > > > 
> > > > * Tao Chen <chen.dylane@linux.dev> wrote:
> > > > 
> > > > > The poll man page says POLLRDNORM is equivalent to POLLIN,
> > > > > so add EPOLLRDNORM here.
> > > > > 
> > > > > Signed-off-by: Tao Chen <chen.dylane@linux.dev>
> > > > > ---
> > > > >   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.
> > 
> > Mind adding this to the changelog, and explain that this patch fixes 
> > this particular poll() functionality and semantics for userspace?
> 
> Off topic, but I think it should return something (either POLLHUP or
> POLLERR) when the event goes to an error state like pinned events are
> not scheduled.

Mind sending a patch for that?

Thanks,

	Ingo
Re: [PATCH linux-next] perf/ring_buffer: Add EPOLLRDNORM flag for poll
Posted by Tao Chen 9 months, 1 week ago 
在 2025/3/14 01:09, Ingo Molnar 写道:
> explain that this patch fixes
> this particular poll() functionality and semantics

will do it, thanks.

-- 
Best Regards
Tao Chen

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