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

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Date:   Tue, 6 Jun 2017 18:25:37 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
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 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.