linux-kernel - Re: [RFC PATCH v2 1/2] kernel/events: Add option to notify through signals on wakeup

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Message-Id: <20170613151613.GA16085@naverao1-tp.localdomain>
Date:   Tue, 13 Jun 2017 20:46:13 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 1/2] kernel/events: Add option to notify through
 signals on wakeup

Hi Jiri,

On 2017/06/13 04:45PM, Jiri Olsa wrote:
> On Tue, Jun 13, 2017 at 05:03:42PM +0530, Naveen N. Rao wrote:
> 
> SNIP
> 
> > diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> > index b1c0b187acfe..e5810b1d74a4 100644
> > --- a/include/uapi/linux/perf_event.h
> > +++ b/include/uapi/linux/perf_event.h
> > @@ -345,7 +345,8 @@ struct perf_event_attr {
> >  				context_switch :  1, /* context switch data */
> >  				write_backward :  1, /* Write ring buffer from end to beginning */
> >  				namespaces     :  1, /* include namespaces data */
> > -				__reserved_1   : 35;
> > +				signal_on_wakeup : 1, /* send signal on wakeup */
> > +				__reserved_1   : 34;
> >  
> >  	union {
> >  		__u32		wakeup_events;	  /* wakeup every n events */
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index 6c4e523dc1e2..73ad30e124e5 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -7362,12 +7362,14 @@ static int __perf_event_overflow(struct perf_event *event,
> >  	 * events
> >  	 */
> >  
> > -	event->pending_kill = POLL_IN;
> > -	if (events && atomic_dec_and_test(&event->event_limit)) {
> > -		ret = 1;
> > -		event->pending_kill = POLL_HUP;
> > +	if (!event->attr.signal_on_wakeup) {
> > +		event->pending_kill = POLL_IN;
> > +		if (events && atomic_dec_and_test(&event->event_limit)) {
> > +			ret = 1;
> > +			event->pending_kill = POLL_HUP;
> >  
> > -		perf_event_disable_inatomic(event);
> > +			perf_event_disable_inatomic(event);
> > +		}
> >  	}
> >  
> >  	READ_ONCE(event->overflow_handler)(event, data, regs);
> > diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
> > index 2831480c63a2..4e7c728569a8 100644
> > --- a/kernel/events/ring_buffer.c
> > +++ b/kernel/events/ring_buffer.c
> > @@ -21,6 +21,9 @@ static void perf_output_wakeup(struct perf_output_handle *handle)
> >  {
> >  	atomic_set(&handle->rb->poll, POLLIN);
> >  
> > +	if (handle->event->attr.signal_on_wakeup)
> > +		handle->event->pending_kill = POLL_IN;
> > +
> 
> since it's signal_on_wakeup, should we also send POLL_HUP for
> perf_event_wakeup calls from perf_event_exit_event?

Yes, I suspect so (though I'm open to changing the name ;)
I haven't handled POLL_HUP properly in this patch, including 
IOC_REFRESH. I will look into that next.

I wanted to know if the overall approach is fine -- between RFC v1 vs.  
this version.

Thanks for the review!
- Naveen