perf/x86-ibs: Extend hw period that triggers overflow
If the last hw period is too short we might hit the irq handler which
biases the results. Thus try to have a max last period that triggers
the sw overflow.
Signed-off-by: Robert Richter <robert.richter@amd.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1333390758-10893-10-git-send-email-robert.richter@amd.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/x86/kernel/cpu/perf_event_amd_ibs.c b/arch/x86/kernel/cpu/perf_event_amd_ibs.c
index 3e32908..cb51a3e 100644
--- a/arch/x86/kernel/cpu/perf_event_amd_ibs.c
+++ b/arch/x86/kernel/cpu/perf_event_amd_ibs.c
@@ -85,8 +85,19 @@
overflow = 1;
}
- if (left > max)
- left = max;
+ /*
+ * If the hw period that triggers the sw overflow is too short
+ * we might hit the irq handler. This biases the results.
+ * Thus we shorten the next-to-last period and set the last
+ * period to the max period.
+ */
+ if (left > max) {
+ left -= max;
+ if (left > max)
+ left = max;
+ else if (left < min)
+ left = min;
+ }
*hw_period = (u64)left;