diff options
| author | Anton Blanchard <anton@samba.org> | 2012-02-15 18:48:22 +0000 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2012-02-29 16:30:49 -0800 |
| commit | 90f91ae1598200e5f650c5ddb1d7165398cf7f5a (patch) | |
| tree | e86aa86b980a21bcc28e4a44cc83ba7886ef3c5f /arch | |
| parent | ae9aea55d123e1091f239833f832de071ff00f22 (diff) | |
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>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/powerpc/kernel/perf_event.c | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/arch/powerpc/kernel/perf_event.c b/arch/powerpc/kernel/perf_event.c index 10a140f82cb..64483fde95c 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); |