On Tue, Jul 07, 2015 at 10:44:37AM -0300, Arnaldo Carvalho de Melo wrote: > Em Tue, Jul 07, 2015 at 10:25:52AM -0300, Arnaldo Carvalho de Melo escreveu: > > Em Tue, Jul 07, 2015 at 11:36:39AM +0300, Adrian Hunter escreveu: > > > To make the event useful for privileged users also, if the > > > context is cpu-wide then the event will also provide the > > > next or previous pid/tid. > > > > <SNIP> > > > > > + /* > > > + * Records a context switch in or out (flagged by > > > + * PERF_RECORD_MISC_SWITCH_OUT). next_prev_pid and next_prev_tid are > > > + * (u32)-1 unless the context is cpu-wide, in which case they are the > > > > Why carry those extra 8 bytes for non priviledged users, all the time > > with -1? > > > Can't userspace cope with this, i.e. we should be able to look for those > > fields when the context is CPU wide, and to not look for them otherwise, > > no? > > To help userspace in places where all it has is the union perf_event, we > can reuse one bit in misc to state that, i.e. > > #define PERF_RECORD_MISC_SWITCH_NEXT_PREV_PID 14 > > For instance.
The other option would be a separate RECORD type, which might be simpler. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
