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From:   Song Liu <songliubraving@fb.com>
To:     Arnaldo Carvalho de Melo <acme@kernel.org>
CC:     Jiri Olsa <jolsa@kernel.org>,
        Stephane Eranian <eranian@google.com>,
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        Kernel Team <Kernel-team@fb.com>,
        "peterz@infradead.org" <peterz@infradead.org>,
        "namhyung@kernel.org" <namhyung@kernel.org>
Subject: Re: [PATCH v2 perf,bpf 08/11] perf, bpf: save btf information as
 headers to perf.data
Thread-Topic: [PATCH v2 perf,bpf 08/11] perf, bpf: save btf information as
 headers to perf.data
Thread-Index: AQHUxMGQlShe9E029kWf9/H0QeuOj6Xg626AgAAx0ACAAARLAIAAAh+A
Date:   Fri, 15 Feb 2019 17:47:58 +0000
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> On Feb 15, 2019, at 9:40 AM, Arnaldo Carvalho de Melo <acme@kernel.org> w=
rote:
>=20
> Em Fri, Feb 15, 2019 at 05:25:01PM +0000, Song Liu escreveu:
>>> On Feb 15, 2019, at 6:26 AM, Arnaldo Carvalho de Melo <acme@redhat.com>=
 wrote:
>>> Em Thu, Feb 14, 2019 at 04:00:09PM -0800, Song Liu escreveu:
>>>> This patch enables perf-record to save btf information as headers to
>>>> perf.data A new header type HEADER_BTF is introduced for this data.
>=20
>>> 	Wouldn't it be better for this HEADER_BTF to be introduced
>>> already as an user space event, Song, see:
>=20
>>> tools/perf/util/event.h
>=20
>>> and:
>=20
>>> tools/perf/util/event.c
>=20
>>> perf_event__synthesize_cpu_map()
>=20
>> BTF would be short living for short living BPF programs. I guess=20
>> saving them as header is easier than merging them with samples.=20
>=20
>> What's the benefit of saving them as user space events?
>=20
> When we work with pipe mode, i.e.:
>=20
> 	perf record -o - | perf report -i -
>=20
> and other combinations (with 'perf script', 'perf inject', etc), we need
> a way to pass the headers to the other side, and the way was via user
> space events.
>=20
> This is something Stephane and Jiri have been discussing recently,
> probably they have more justifications, Stephane, Jiri?
>=20
> - Arnaldo

I see. In this case, we will need some synchronization between main
thread and the polling thread, as they are both writing to the same
pipe.=20

Thanks,
Song