Re: [PATCH] perf/core: Emit PERF_RECORD_LOST for pinned events

From: Namhyung Kim
Date: Mon Jan 18 2021 - 09:19:05 EST

Hi Peter,

On Mon, Jan 18, 2021 at 7:11 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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.