> On Nov 24, 2020, at 3:43 PM, Song Liu <[email protected]> wrote:
>
>
>
>> On Nov 24, 2020, at 11:51 AM, Jiri Olsa <[email protected]> wrote:
>>
>> On Wed, Nov 18, 2020 at 08:50:46PM -0800, Song Liu wrote:
>>
>> SNIP
>>
>>> +static int bpf_program_profiler__install_pe(struct evsel *evsel, int cpu,
>>> + int fd)
>>> +{
>>> + struct bpf_prog_profiler_bpf *skel = evsel->bpf_counter.skel;
>>> +
>>> + return bpf_map_update_elem(bpf_map__fd(skel->maps.events),
>>> + &cpu, &fd, BPF_ANY);
>>> +}
>>> +
>>> +struct bpf_counter_ops bpf_program_profiler_ops = {
>>> + .load = bpf_program_profiler__load,
>>> + .enable = bpf_program_profiler__enable,
>>> + .read = bpf_program_profiler__read,
>>> + .destroy = bpf_program_profiler__destroy,
>>> + .install_pe = bpf_program_profiler__install_pe,
>>> +};
>>
>> hum, what's the point of this ops? you plan some other ops?
>> we could just define stat callbacks right?
Which callbacks do you mean here? I would like to try that as
well.
Thanks,
Song
>
> I do have other ideas using BPF program to aggregate perf event
> counts. This ops provides common interface for different BPF
> extensions to evsel.
>
>>
>>> +SEC("fentry/XXX")
>>> +int BPF_PROG(fentry_XXX)
>>> +{
>>> + u32 key = bpf_get_smp_processor_id();
>>> + struct bpf_perf_event_value reading;
>>> + struct bpf_perf_event_value *ptr;
>>> + u32 zero = 0;
>>> + long err;
>>> +
>>> + /* look up before reading, to reduce error */
>>> + ptr = bpf_map_lookup_elem(&fentry_readings, &zero);
>>> + if (!ptr)
>>> + return 0;
>>> +
>>> + err = bpf_perf_event_read_value(&events, key, &reading,
>>> + sizeof(reading));
>>> + if (err)
>>> + return 0;
>>> +
>>> + *ptr = reading;
>>> + return 0;
>>> +}
>>
>> so currently it's one extra bpf program for each event,
>> but it seems bad for multiple events stat.. could we
>> just have one program that would read and process all events?
>
> Multiple fentry programs should not be too expensive. Current design
> extends evsel, so it is a cleaner implementation. We can evaluate the
> difference of these two designs by comparing this with
> "bpftool prog profile".
>
> Thanks,
> Song
