From: Peter Zijlstra <peterz@infradead.org>
To: Namhyung Kim <namhyung@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>,
Jiri Olsa <jolsa@redhat.com>, Ingo Molnar <mingo@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Andi Kleen <ak@linux.intel.com>, Ian Rogers <irogers@google.com>,
Stephane Eranian <eranian@google.com>,
Song Liu <songliubraving@fb.com>
Subject: Re: [PATCHSET v2 0/3] perf stat: Enable BPF counters with --for-each-cgroup
Date: Thu, 17 Jun 2021 00:32:12 +0200 [thread overview]
Message-ID: <20210616223212.GE4272@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <CAM9d7cj2UhQsd2vx8_C8C_CEW2QQbzs741jCn7f7g-e0i9OiOg@mail.gmail.com>
On Wed, Jun 16, 2021 at 09:33:42AM -0700, Namhyung Kim wrote:
> > That seems unfortunate; there's no bpf helper to iterate cgroup
> > hierarchy?
>
> I couldn't find one..
Song, is that something that would make sense to have?
> > > * there's no reliable way to trigger running the BPF program
> >
> > You can't attach to the PERF_COUNT_SW_CGROUP_SWITCHES event?
>
> I did it. But the BPF test run seems not to work with perf_event.
> So it needs to trigger a cgroup switch manually..
AFAICT it should be possible to set a bpf prog on a software event.
perf_event_set_bpf_prog() will take the first branch
(!perf_event_is_tracing()) and call perf_event_set_bpf_handler().
That should then result in running the bpf program every time the event
would generate a sample.
So if you configure the event to sample on every single event, it should
then run your program every time.
This is all from looking at the code, because I really can't operate any
of that for real. I suspect Song can help out.
The alternative is to attach a BPF program to the sched_switch
tracepoint and do the cgroup filter in BPF.
next prev parent reply other threads:[~2021-06-16 22:32 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-15 1:17 [PATCHSET v2 0/3] perf stat: Enable BPF counters with --for-each-cgroup Namhyung Kim
2021-06-15 1:17 ` [PATCH 1/3] perf tools: Add read_cgroup_id() function Namhyung Kim
2021-06-15 1:17 ` [PATCH 2/3] perf tools: Add cgroup_is_v2() helper Namhyung Kim
2021-06-15 1:17 ` [PATCH 3/3] perf stat: Enable BPF counter with --for-each-cgroup Namhyung Kim
2021-06-16 15:14 ` [PATCHSET v2 0/3] perf stat: Enable BPF counters " Peter Zijlstra
2021-06-16 16:33 ` Namhyung Kim
2021-06-16 22:32 ` Peter Zijlstra [this message]
2021-06-17 6:33 ` Song Liu
2021-06-22 1:43 ` Namhyung Kim
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