Re: [PATCH] perf/core: Add a tracepoint for perf sampling

[Wangnan (F)]

On 2016/7/30 2:05, Brendan Gregg wrote:
> On Tue, Jul 19, 2016 at 4:20 PM, Brendan Gregg <bgregg@xxxxxxxxxxx> wrote:
> > When perf is performing hrtimer-based sampling, this tracepoint can be used
> > by BPF to run additional logic on each sample. For example, BPF can fetch
> > stack traces and frequency count them in kernel context, for an efficient
> > profiler.
> Any comments on this patch? Thanks,
>
> Brendan

Sorry for the late.

I think it is a useful feature. Could you please provide an example
to show how to use it in perf?

If I understand correctly, I can have a BPF script run 99 times per
second using

  # perf -e cpu-clock/freq=99/ -e mybpf.c ...

And in mybpf.c, attach a BPF script on the new tracepoint. Right?

Also, since we already have timer:hrtimer_expire_entry, please provide
some further information about why we need a new tracepoint.

Thank you.