lkml.org 
[lkml]   [2012]   [Feb]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[ 06/73] powerpc/perf: power_pmu_start restores incorrect values, breaking frequency events
3.0-stable review patch.  If anyone has any objections, please let me know.

------------------
From: Anton Blanchard <anton@samba.org>

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(-)
--- 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_
{
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->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);



\
 
 \ /
  Last update: 2012-02-28 02:39    [from the cache]
©2003-2014 Jasper Spaans. Advertise on this site