linux-kernel - Re: [RFC PATCH 1/1] kernel/events: Introduce IOC_COUNT

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Date:   Tue, 6 Jun 2017 23:02:31 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/1] kernel/events: Introduce IOC_COUNT_RECORDS

On 2017/06/06 06:25PM, Peter Zijlstra wrote:
> On Tue, Jun 06, 2017 at 08:21:18PM +0530, Naveen N. Rao wrote:
> > Many perf sideband events (context switches, namespaces, ...) are useful
> > by themselves without the need for subscribing to any overflow events.
> > However, it is not possible to subscribe for notifications when such
> > records are logged into the ring buffer. Introduce IOC_COUNT_RECORDS as
> > a way to request this.
> > 
> > With IOC_COUNT_RECORDS set, IOC_REFRESH takes the number of records
> > after which to generate a notification, rather than the number of
> > overflow events.
> > 
> > Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
> > ---
> >  include/linux/perf_event.h      |  1 +
> >  include/uapi/linux/perf_event.h |  1 +
> >  kernel/events/core.c            | 16 +++++++++++++++-
> >  kernel/events/ring_buffer.c     |  9 +++++++++
> >  4 files changed, 26 insertions(+), 1 deletion(-)
> > 
> > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> > index 24a635887f28..016f2da2bba7 100644
> > --- a/include/linux/perf_event.h
> > +++ b/include/linux/perf_event.h
> > @@ -683,6 +683,7 @@ struct perf_event {
> >  	struct irq_work			pending;
> >  
> >  	atomic_t			event_limit;
> > +	bool				count_records;
> 
> This is an instant nack ;-) Never, that is _never_ use bool in composite
> types.

Ouch! Sorry.
I did briefly consider labeling this 'EARLY RFC', but that still 
wouldn't have done justice :/

Thanks for the review,
- Naveen