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From a5e7847241035f1293439ae2422c9e19271c0c24 Mon Sep 17 00:00:00 2001
From: Anton Blanchard <anton@samba.org>
Date: Wed, 15 Feb 2012 18:48:22 +0000
Subject: [PATCH 02/72] powerpc/perf: power_pmu_start restores incorrect
values, breaking frequency events
commit 9a45a9407c69d068500923480884661e2b9cc421 upstream.
perf on POWER stopped working after commit e050e3f0a71b (perf: Fix
broken interrupt rate throttling). That patch exposed a bug in
the POWER perf_events code.
Since the PMCs count upwards and take an exception when the top bit
is set, we want to write 0x80000000 - left in power_pmu_start. We were
instead programming in left which effectively disables the counter
until we eventually hit 0x80000000. This could take seconds or longer.
With the patch applied I get the expected number of samples:
SAMPLE events: 9948
Signed-off-by: Anton Blanchard <anton@samba.org>
Acked-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/powerpc/kernel/perf_event.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/kernel/perf_event.c b/arch/powerpc/kernel/perf_event.c
index 10a140f..64483fd 100644
--- a/arch/powerpc/kernel/perf_event.c
+++ b/arch/powerpc/kernel/perf_event.c
@@ -865,6 +865,7 @@ static void power_pmu_start(struct perf_event *event, int ef_flags)
{
unsigned long flags;
s64 left;
+ unsigned long val;
if (!event->hw.idx || !event->hw.sample_period)
return;
@@ -880,7 +881,12 @@ static void power_pmu_start(struct perf_event *event, int ef_flags)
event->hw.state = 0;
left = local64_read(&event->hw.period_left);
- write_pmc(event->hw.idx, left);
+
+ val = 0;
+ if (left < 0x80000000L)
+ val = 0x80000000L - left;
+
+ write_pmc(event->hw.idx, val);
perf_event_update_userpage(event);
perf_pmu_enable(event->pmu);
--
1.7.9.4
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