On Mon, Aug 05, 2019 at 10:16:12AM +0300, Alexander Shishkin wrote: > In some cases, ordinary (non-AUX) events can generate data for AUX events. > For example, PEBS events can come out as records in the Intel PT stream > instead of their usual DS records, if configured to do so. > > One requirement for such events is to consistently schedule together, to > ensure that the data from the "AUX source" events isn't lost while their > corresponding AUX event is not scheduled. We use grouping to provide this > guarantee: an "AUX source" event can be added to a group where an AUX event > is a group leader, and provided that the former supports writing to the > latter.
Two niggles -- and sorry for not bringing those up sooner: > diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h > index 7198ddd0c6b1..213cae95e713 100644 > --- a/include/uapi/linux/perf_event.h > +++ b/include/uapi/linux/perf_event.h > @@ -374,7 +374,8 @@ struct perf_event_attr { > namespaces : 1, /* include namespaces data > */ > ksymbol : 1, /* include ksymbol events > */ > bpf_event : 1, /* include bpf events */ > - __reserved_1 : 33; > + aux_source : 1, /* generate AUX records > instead of events */ > + __reserved_1 : 32; > > union { > __u32 wakeup_events; /* wakeup every n events */ The name: "aux_source" seems to imply that we change the source to 'aux', while in fact it is the destination we change. So we want to %s/aux_source/aux_output/ on the whole thing? > + /* > + * Our group leader must be an aux event if we want to be > + * an aux_source. This way, the aux event will precede its > + * aux_source events in the group, and therefore will always > + schedule first. > + */ You fudged the comment there.