Re: [PATCH] perf_events: improve x86 event scheduling (v5)

[Peter Zijlstra <peterz@infradead.org>]

On Mon, 2010-01-18 at 14:43 +0100, Frederic Weisbecker wrote:
> 
> Shouldn't we actually use the core based pmu->enable(),disable()
> model called from kernel/perf_event.c:event_sched_in(),
> like every other events, where we can fill up the queue of hardware
> events to be scheduled, and then call a hw_check_constraints()
> when we finish a group scheduling? 

Well the thing that makes hw_perf_group_sched_in() useful is that you
can add a bunch of events and not have to reschedule for each one, but
instead do a single schedule pass.

That said you do have a point, maybe we can express this particular
thing differently.. maybe a pre and post group call like:

 void hw_perf_group_sched_in_begin(struct pmu *pmu)
 int  hw_perf_group_sched_in_end(struct pmu *pmu)

That way we know we need to track more state for rollback and can give
the pmu implementation leeway to delay scheduling/availablility tests.

Paul, would that work for you too?

Then there's still the question of having events of multiple hw pmus in
a single group, I'd be perfectly fine with saying that's not allowed,
what to others think?