Subject: Re: How about limiting refresh ioctl to sampling events ?
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Franck Bui-Huu <vagabon.xyz@gmail.com>
Cc: lkml <linux-kernel@vger.kernel.org>,
        Francis Moreau <francis.moro@gmail.com>
In-Reply-To: <m3vd3o5g9u.fsf@gmail.com>
References: <m3zkt05h3w.fsf@gmail.com> <1290517646.2072.403.camel@laptop>
	 <m3vd3o5g9u.fsf@gmail.com>
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Date: Tue, 23 Nov 2010 14:46:20 +0100
Message-ID: <1290519980.2072.404.camel@laptop>
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On Tue, 2010-11-23 at 14:19 +0100, Franck Bui-Huu wrote:
> Peter Zijlstra <a.p.zijlstra@chello.nl> writes:
> 
> > On Tue, 2010-11-23 at 14:01 +0100, Franck Bui-Huu wrote:
> >> Hello Peter,
> >> 
> >> I'm looking at the perf event stuff and wondering if
> >
> >> perf_event_refresh() should be limited to sampling events.
> >> 
> >> Does the following make sense ?
> >> 
> >> diff --git a/kernel/perf_event.c b/kernel/perf_event.c
> >> index 3b105e0..1a90a6c 100644
> >> --- a/kernel/perf_event.c
> >> +++ b/kernel/perf_event.c
> >> @@ -1072,7 +1072,7 @@ static int perf_event_refresh(struct perf_event *event, int refresh)
> >>  	/*
> >>  	 * not supported on inherited events
> >>  	 */
> >> -	if (event->attr.inherit)
> >> +	if (event->attr.inherit || !event->attr.sample_period)
> >>  		return -EINVAL;
> >>  
> >>  	atomic_add(refresh, &event->event_limit);
> >
> > Yes it does, please submit as a proper patch.
> 
> Ok.
> 
> I'm also wondering if you would accept a second patch which will
> introduce:
> 
> static inline bool is_sampling_event(struct perf_event *event)
> {
>         return event->attr.sample_period != 0;
> }
> 
> That would make the code slighlty easier to read IMHO.
> 

Sure, Francis might want that too, he found another something like this.
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