From: Peter Zijlstra <peterz@infradead.org>
To: Namhyung Kim <namhyung@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>,
Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>,
Song Liu <songliubraving@fb.com>, Jiri Olsa <jolsa@kernel.org>,
Martin KaFai Lau <kafai@fb.com>, Yonghong Song <yhs@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@kernel.org>, Hao Luo <haoluo@google.com>,
Stanislav Fomichev <sdf@google.com>,
LKML <linux-kernel@vger.kernel.org>,
bpf@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
Arnaldo Carvalho de Melo <acme@kernel.org>
Subject: Re: [PATCH bpf-next 1/2] bpf/perf: Call perf_prepare_sample() before bpf_prog_run()
Date: Thu, 22 Dec 2022 21:16:05 +0100 [thread overview]
Message-ID: <Y6S7BcblAHO4nQTf@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAM9d7cj=iuxhLndNMBMeff6Ayp2hLfdz+6CHsZL7g213aWbUYQ@mail.gmail.com>
On Thu, Dec 22, 2022 at 09:34:42AM -0800, Namhyung Kim wrote:
> Sorry about that. Let me rephrase it like below:
>
> With bpf_cast_to_kern_ctx(), BPF programs attached to a perf event
> can access perf sample data directly from the ctx.
This is the bpf_prog_run() in bpf_overflow_handler(), right?
> But the perf sample
> data is not fully prepared at this point, and some fields can have invalid
> uninitialized values. So it needs to call perf_prepare_sample() before
> calling the BPF overflow handler.
It never was, why is it a problem now?
> But just calling perf_prepare_sample() can be costly when the BPF
So you potentially call it twice now, how's that useful?
next prev parent reply other threads:[~2022-12-22 20:16 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-20 22:01 [PATCH bpf-next 0/2] bpf: Allow access to perf sample data (v2) Namhyung Kim
2022-12-20 22:01 ` [PATCH bpf-next 1/2] bpf/perf: Call perf_prepare_sample() before bpf_prog_run() Namhyung Kim
2022-12-22 12:55 ` Peter Zijlstra
2022-12-22 13:17 ` Daniel Borkmann
2022-12-22 17:34 ` Namhyung Kim
2022-12-22 20:16 ` Peter Zijlstra [this message]
2022-12-22 22:25 ` Namhyung Kim
2022-12-23 7:53 ` Jiri Olsa
2022-12-27 23:19 ` Namhyung Kim
2022-12-20 22:01 ` [PATCH bpf-next 2/2] selftests/bpf: Add perf_event_read_sample test cases Namhyung Kim
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