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

From: "Wangnan (F)" <[email-masked]>
Date: Thu, 22 Oct 2015 11:12:16 +0800

On 2015/10/22 11:09, Alexei Starovoitov wrote:
> On 10/21/15 6:56 PM, Wangnan (F) wrote:
>>> One alternative solution I can image is to attach a BPF program
>>> at sampling like kprobe, and return 0 if we don't want sampling
>>> take action. Thought?
>>
>> Do you think attaching BPF programs to sampling is an acceptable idea?
>
> If you mean to extend 'filter' concept to sampling events?
> So instead of soft_disable of non-local events, you'll attach bpf
> program to sampling events and use map lookup to decide whether
> to filter out or not such sampling event?

Yes.

> What pt_regs would be in such case?
>

Sampling is based on interruption. We can use pt_reg captured by the IRQ 
handler,
or we can simply pass NULL to those BPF program.

Thank you.