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SubjectRe: [PATCH v2 1/2] kernel/events: Add option to notify through signals on wakeup
Hi Vince,
Thanks for taking a look.

On 2017/08/03 01:57PM, Vince Weaver wrote:
> On Tue, 1 Aug 2017, Naveen N. Rao wrote:
>
> > Add a new option 'signal_on_wakeup' to request for a signal to be
> > delivered on ring buffer wakeup controlled through watermark and
> > {wakeup_events, wakeup_watermark}. HUP is signaled on exit.
> >
> > Setting signal_on_wakeup disables use of IOC_REFRESH to control signal
> > delivery, instead relying on IOC_ENABLE/DISABLE.
>
> so I probably missed the original thread on this new interface, but why is
> IOC_REFRESH not being used?

IOC_REFRESH is used to control the number of overflows before disabling
the event. It works outside of perf_event_attr in the sense that it
enables POLL_IN on each overflow and user specifies the number of
overflows after which to disable the event as part of the ioctl (when
HUP is signaled).

However, signal_on_wakeup is designed to work with the values in the
perf_event_attr structure itself. wakeup_events controls the number of
events after which to signal POLL_IN. signal_on_wakeup itself needs to
be specified in the perf_event_attr. As such, I felt it is better to
have all control through perf_event_attr.

But, if you think having IOC_REFRESH available in this scenario is
useful, we can revisit this. Ideally, we would have separate ioctls to
control signal delivery separate from perf_event_attr, but I am not sure
how useful that would be.

>
> For new interfaces like this it's also nice to have some text that can be
> added to the perf_event_open() manpage, especially if there's weird
> conditions like this.

Sure -- I will send an update to the manpage once this series gets
accepted.

Thanks,
Naveen

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