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From:   Namhyung Kim <namhyung@kernel.org>
Date:   Mon, 18 Jan 2021 20:44:20 +0900
Message-ID: <CAM9d7cgr+Vxq_SnEkSO5zU0QN-X6-LLJDKUfE4C72Nomnrr=+Q@mail.gmail.com>
Subject: Re: [PATCH] perf/core: Emit PERF_RECORD_LOST for pinned events
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Arnaldo Carvalho de Melo <acme@kernel.org>,
        Jiri Olsa <jolsa@redhat.com>, Ingo Molnar <mingo@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Stephane Eranian <eranian@google.com>,
        Andi Kleen <ak@linux.intel.com>,
        Ian Rogers <irogers@google.com>,
        Alexey Alexandrov <aalexand@google.com>
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Hi Peter,

On Mon, Jan 18, 2021 at 7:11 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Mon, Jan 18, 2021 at 12:43:23PM +0900, Namhyung Kim wrote:
> > As of now we silently ignore pinned events when it's failed to be
> > scheduled and make it error state not try to schedule it again.
> > That means we won't get any samples for the event.
> >
> > But there's no way for users to notice and respond to it.  Let's
> > emit a lost event with a new misc bit to indicate this situation.
>
> Users should get a read(2) error IIRC, does that not work?

Ah, right.  maybe I'm too specific to perf record's perspective.

In perf record, it doesn't use read(2) so I thought it should
have the information in the stream of sample data.

Thanks,
Namhyung