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

From: Namhyung Kim
Date: Mon Jan 18 2021 - 22:12:56 EST

Hi Andi,

On Tue, Jan 19, 2021 at 11:47 AM Andi Kleen <ak@xxxxxxxxxxxxxxx> wrote:
> > > I don't think I object to having an even in the stream, but your LOST
> > > event is unfortunate in that it itself can get lost when there's no
> > > space in the buffer (which arguably is unlikely, but still).
> > >
> > > So from that point of view, I think overloading LOST is not so very nice
> > > for this.
> >
> > But anything can get lost in case of no space.
> > Do you want to use something other than the LOST event?
> Could always reserve the last entry in the ring buffer for a LOST event,
> that would guarantee you can always get one out.

A problem is that we can have more than one event that failed.

In my understanding, we keep the lost count and add a LOST event
when there's a space later. So probably we can keep a list of the
failed events and do similar for each event. Or just use a single
event to notify some number of events were failed.