Re: [PATCH V5 1/1] bpf: control events stored in PERF_EVENT_ARRAY maps trace data output when perf sampling

[Peter Zijlstra]

On Wed, Oct 21, 2015 at 07:34:28PM +0800, Wangnan (F) wrote:
> >If you want to actually disable the event: pmu->stop() will make it
> >stop, and you can restart using pmu->start().xiezuo
> 
> I also prefer totally disabling event because our goal is to reduce
> sampling overhead as mush as possible. However, events in perf is
> CPU bounded, one event in perf cmdline becomes multiple 'perf_event'
> in kernel in multi-core system. Disabling/enabling events on all CPUs
> by a BPF program a hard task due to racing, NMI, ...

But eBPF perf events must already be local afaik. Look at the
constraints perf_event_read_local() places on the events.
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