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From:   Song Liu <songliubraving@fb.com>
To:     Jiri Olsa <jolsa@redhat.com>
CC:     Song Liu <song@kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        Kernel Team <Kernel-team@fb.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        "jolsa@kernel.org" <jolsa@kernel.org>
Subject: Re: [PATCH v2 3/3] perf-stat: introduce config
 stat.bpf-counter-events
Thread-Topic: [PATCH v2 3/3] perf-stat: introduce config
 stat.bpf-counter-events
Thread-Index: AQHXK0YG4LdD7IbPc0ehmtAjm2+fxaqqg16AgABRlYCAAAtnAIAAAjCA
Date:   Thu, 8 Apr 2021 17:28:10 +0000
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> On Apr 8, 2021, at 10:20 AM, Jiri Olsa <jolsa@redhat.com> wrote:
>=20
> On Thu, Apr 08, 2021 at 04:39:33PM +0000, Song Liu wrote:
>>=20
>>=20
>>> On Apr 8, 2021, at 4:47 AM, Jiri Olsa <jolsa@redhat.com> wrote:
>>>=20
>>> On Tue, Apr 06, 2021 at 05:36:01PM -0700, Song Liu wrote:
>>>> Currently, to use BPF to aggregate perf event counters, the user uses
>>>> --bpf-counters option. Enable "use bpf by default" events with a confi=
g
>>>> option, stat.bpf-counter-events. This is limited to hardware events in
>>>> evsel__hw_names.
>>>>=20
>>>> This also enables mixed BPF event and regular event in the same sesssi=
on.
>>>> For example:
>>>>=20
>>>>  perf config stat.bpf-counter-events=3Dinstructions
>>>>  perf stat -e instructions,cs
>>>>=20
>>>=20
>>> so if we are mixing events now, how about uing modifier for bpf counter=
s,
>>> instead of configuring .perfconfig list we could use:
>>>=20
>>> perf stat -e instructions:b,cs
>>>=20
>>> thoughts?
>>>=20
>>> the change below adds 'b' modifier and sets 'evsel::bpf_counter',
>>> feel free to use it
>>=20
>> I think we will need both 'b' modifier and .perfconfig configuration.=20
>> For systems with BPF-managed perf events running in the background,=20
>=20
> hum, I'm not sure I understand what that means.. you mean there
> are tools that run perf stat so you don't want to change them?

We have tools that do perf_event_open(). I will change them to use=20
BPF managed perf events for "cycles" and "instructions". Since these=20
tools are running 24/7, perf-stat on the system should use BPF managed
"cycles" and "instructions" by default.=20

>=20
>> .perfconfig makes sure perf-stat sessions will share PMCs with these=20
>> background monitoring tools. 'b' modifier, on the other hand, is useful
>> when the user knows there is opportunity to share the PMCs.=20
>>=20
>> Does this make sense?=20
>=20
> if there's reason for that then sure.. but let's not limit that just
> on HARDWARE events only.. there are RAW events with the same demand
> for this feature.. why don't we let user define any event for this?

I haven't found a good way to config RAW events. I guess RAW events=20
could use 'b' modifier?=20

Thanks,
Song=