perf/x86: Reduce stack usage of x86_schedule_events()

x86_schedule_events() caches event constraints on the stack during
scheduling.  Given the number of possible events, this is 512 bytes of
stack; since it can be invoked under schedule() under god-knows-what,
this is causing stack blowouts.

Trade some space usage for stack safety: add a place to cache the
constraint pointer to struct perf_event.  For 8 bytes per event (1% of
its size) we can save the giant stack frame.

This shouldn't change any aspect of scheduling whatsoever and while in
theory the locality's a tiny bit worse, I doubt we'll see any
performance impact either.

Tested: `perf stat whatever` does not blow up and produces
results that aren't hugely obviously wrong.  I'm not sure how to run
particularly good tests of perf code, but this should not produce any
functional change whatsoever.

Signed-off-by: Andrew Hunter <ahh@google.com>
Reviewed-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1369332423-4400-1-git-send-email-ahh@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 4bc57d017fc..33e8d65836d 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -113,6 +113,8 @@ struct hw_perf_event_extra {
 	int		idx;	/* index in shared_regs->regs[] */
 };
 
+struct event_constraint;
+
 /**
  * struct hw_perf_event - performance event hardware details:
  */
@@ -131,6 +133,8 @@ struct hw_perf_event {
 
 			struct hw_perf_event_extra extra_reg;
 			struct hw_perf_event_extra branch_reg;
+
+			struct event_constraint *constraint;
 		};
 		struct { /* software */
 			struct hrtimer	hrtimer;