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Date: Tue, 30 Aug 2016 08:47:24 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Jiri Olsa <jolsa@redhat.com>
Cc: Vegard Nossum <vegard.nossum@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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Subject: Re: [tip:perf/core] perf/core: Check return value of the
 perf_event_read() IPI
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On Mon, Aug 29, 2016 at 08:58:41PM +0200, Jiri Olsa wrote:
> couldn't we just call smp_call_function_single(cpu_to_read, __perf_event_read, ...
> once we read oncpu != -1 ?
> 

Yes, and at that point we can simply revert this WARN, because that is
exactly the same.

Which I think is what I'm going to do.

If oncpu is not valid, the sched_out that made it invalid will have
updated the event count and we're good.

All I'll leave is an explicit comment that we've ignored the
smp_call_function_single() return value on purpose.