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

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Date:   Tue, 13 Jun 2017 16:45:07 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.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

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?

jirka