On Wed, Sep 21, 2016 at 07:43:28PM -0500, Paul Clarke wrote: > On 09/20/2016 03:56 PM, Vineet Gupta wrote: > >On 09/01/2016 01:33 AM, Peter Zijlstra wrote: > >>>- is that what perf event grouping is ? > >> > >>Again, nope. Perf event groups are single counter (so no implicit > >>addition) that are co-scheduled on the PMU. > > > >I'm not sure I understand - does this require specific PMU/arch support - as in > >multiple conditions feeding to same counter. > > My read is that is that what Peter meant was that each event in the > perf event group is a single counter, so all the events in the group > are counted simultaneously. (No multiplexing.) Right, sorry for the poor wording. > >Again when you say co-scheduled what do you mean - why would anyone use the event > >grouping - is it when they only have 1 counter and they want to count 2 > >conditions/events at the same time - isn't this same as event multiplexing ? > > I'd say it's the converse of multiplexing. Instead of mapping > multiple events to a single counter, perf event groups map a set of > events each to their own counter, and they are active simultaneously. > I suppose it's possible for the _groups_ to be multiplexed with other > events or groups, but the group as a whole will be scheduled together, > as a group. Correct. Each events get their own hardware counter. Grouped events are co-scheduled on the hardware. You can multiplex groups. But if one event in a group is schedule, they all must be.
