| From f56029410a13cae3652d1f34788045c40a13ffc7 Mon Sep 17 00:00:00 2001 |
| From: Anton Blanchard <anton@samba.org> |
| Date: Thu, 29 May 2014 08:15:38 +1000 |
| Subject: powerpc/perf: Never program book3s PMCs with values >= 0x80000000 |
| |
| From: Anton Blanchard <anton@samba.org> |
| |
| commit f56029410a13cae3652d1f34788045c40a13ffc7 upstream. |
| |
| We are seeing a lot of PMU warnings on POWER8: |
| |
| Can't find PMC that caused IRQ |
| |
| Looking closer, the active PMC is 0 at this point and we took a PMU |
| exception on the transition from negative to 0. Some versions of POWER8 |
| have an issue where they edge detect and not level detect PMC overflows. |
| |
| A number of places program the PMC with (0x80000000 - period_left), |
| where period_left can be negative. We can either fix all of these or |
| just ensure that period_left is always >= 1. |
| |
| This patch takes the second option. |
| |
| Signed-off-by: Anton Blanchard <anton@samba.org> |
| Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| arch/powerpc/perf/core-book3s.c | 17 ++++++++++++++++- |
| 1 file changed, 16 insertions(+), 1 deletion(-) |
| |
| --- a/arch/powerpc/perf/core-book3s.c |
| +++ b/arch/powerpc/perf/core-book3s.c |
| @@ -472,7 +472,22 @@ static void power_pmu_read(struct perf_e |
| } while (local64_cmpxchg(&event->hw.prev_count, prev, val) != prev); |
| |
| local64_add(delta, &event->count); |
| - local64_sub(delta, &event->hw.period_left); |
| + |
| + /* |
| + * A number of places program the PMC with (0x80000000 - period_left). |
| + * We never want period_left to be less than 1 because we will program |
| + * the PMC with a value >= 0x800000000 and an edge detected PMC will |
| + * roll around to 0 before taking an exception. We have seen this |
| + * on POWER8. |
| + * |
| + * To fix this, clamp the minimum value of period_left to 1. |
| + */ |
| + do { |
| + prev = local64_read(&event->hw.period_left); |
| + val = prev - delta; |
| + if (val < 1) |
| + val = 1; |
| + } while (local64_cmpxchg(&event->hw.period_left, prev, val) != prev); |
| } |
| |
| /* |