Messages in this thread Patch in this message | | | Date | Thu, 13 Jul 2017 20:07:31 +0530 | From | "Naveen N. Rao" <> | Subject | Re: [PATCH 1/2] kernel/events: Add option to notify through signals on wakeup |
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On 2017/07/12 01:46PM, Peter Zijlstra wrote: > On Mon, Jun 19, 2017 at 08:01:07PM +0530, Naveen N. Rao wrote: > > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > index 6c4e523dc1e2..812fcfc767f4 100644 > > --- a/kernel/events/core.c > > +++ b/kernel/events/core.c > > @@ -2679,7 +2679,8 @@ static int _perf_event_refresh(struct perf_event *event, int refresh) > > /* > > * not supported on inherited events > > That comment wants updating to explain the signal crud..
Ok sure. Will do.
> > > */ > > - if (event->attr.inherit || !is_sampling_event(event)) > > + if (event->attr.inherit || event->attr.signal_on_wakeup || > > + !is_sampling_event(event)) > > return -EINVAL; > > > > atomic_add(refresh, &event->event_limit); > > > @@ -7362,12 +7362,15 @@ static int __perf_event_overflow(struct perf_event *event, > > * events > > */ > > > > + if (!event->attr.signal_on_wakeup) { > > + int events = atomic_read(&event->event_limit); > > + 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); > > + } > > } > > So even without event_limit (IOC_REFRESH) this would've generated > SIGIO:POLL_IN.
Yes, this still does if signal_on_wakeup isn't set. However, if signal_on_wakeup is set, we follow the ring buffer notification which will generate a POLL_IN controlled by {wakeup_events, wakeup_watermark}.
> > > > > READ_ONCE(event->overflow_handler)(event, data, regs); > > @@ -10408,6 +10411,7 @@ perf_event_exit_event(struct perf_event *child_event, > > perf_group_detach(child_event); > > list_del_event(child_event, child_ctx); > > child_event->state = PERF_EVENT_STATE_EXIT; /* is_event_hup() */ > > + child_event->pending_kill = POLL_HUP; > > This looks like an undocumented change..
Yes, sorry - I should have added a note.
This comes from Jiri's feedback that if user chooses to have a signal delivered on ring buffer wakeup, we should also send a HUP on exit.
> > > raw_spin_unlock_irq(&child_ctx->lock); > > > > /* > > 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; > > + > > And this is the bit that generates SIGIO:POLL_IN on wakeup.
Yes.
Thanks, Naveen
> > > handle->event->pending_wakeup = 1; > > irq_work_queue(&handle->event->pending); > > } > > -- > > 2.13.1 > > >
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