diff options
| author | Anton Blanchard <anton@samba.org> | 2014-05-29 08:15:38 +1000 |
|---|---|---|
| committer | Jiri Slaby <jslaby@suse.cz> | 2014-07-18 15:51:20 +0200 |
| commit | a348a994e4312b0566c72ec49d72a4a754e267d8 (patch) | |
| tree | 8eccd7d283299937539f4b04fa1823bd164fce29 /arch | |
| parent | 8c1eb0393ccc6ab3e79fae8a1e7dcd538f0af010 (diff) | |
powerpc/perf: Never program book3s PMCs with values >= 0x80000000
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: Jiri Slaby <jslaby@suse.cz>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/powerpc/perf/core-book3s.c | 17 |
1 files changed, 16 insertions, 1 deletions
diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c index 29b89e863d7c..023f5adf27b8 100644 --- a/arch/powerpc/perf/core-book3s.c +++ b/arch/powerpc/perf/core-book3s.c @@ -851,7 +851,22 @@ static void power_pmu_read(struct perf_event *event) } 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); } /* |