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

On Wed, Oct 21, 2015 at 02:19:49PM -0700, Alexei Starovoitov wrote:

quoted

Urgh, that's still horridly inconsistent. Can we please come up with a
consistent interface to perf?

My suggestion was to do ioctl(enable/disable) of events from userspace
after receiving notification from kernel via my bpf_perf_event_output()
helper.

Wangnan's argument was that display refresh happens often and it's fast,
so the time taken by user space to enable events on all cpus is too
slow and ioctl does ipi and disturbs other cpus even more.
So soft_disable done by the program to enable/disable particular events
on all cpus kinda makes sense.

And this all makes me think I still have no clue what you're all trying
to do here.

Who cares about display updates and why. And why should there be an
active userspace part to eBPF programs?