[34-longterm 193/247] perf, powerpc: Handle events that raise an exception without overflowing

Paul Gortmaker
2011-06-23T17:47:16Z

From: Anton Blanchard <anton@samba.org>

-------------------
This is a commit scheduled for the next v2.6.34 longterm release.
If you see a problem with using this for longterm, please comment.
-------------------

commit 0837e3242c73566fc1c0196b4ec61779c25ffc93 upstream.

Events on POWER7 can roll back if a speculative event doesn't
eventually complete. Unfortunately in some rare cases they will
raise a performance monitor exception. We need to catch this to
ensure we reset the PMC. In all cases the PMC will be 256 or less
cycles from overflow.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20110309143842.6c22845e@kryten>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
arch/powerpc/include/asm/reg.h | 1 +
arch/powerpc/kernel/perf_event.c | 24 +++++++++++++++++++++++-
2 files changed, 24 insertions(+), 1 deletions(-)

diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index 5572e86..f2ac5a6 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -864,6 +864,7 @@
#define PV_970 0x0039
#define PV_POWER5 0x003A
#define PV_POWER5p 0x003B
+#define PV_POWER7 0x003F
#define PV_970FX 0x003C
#define PV_630 0x0040
#define PV_630p 0x0041
diff --git a/arch/powerpc/kernel/perf_event.c b/arch/powerpc/kernel/perf_event.c
index 08460a2..7a3b2d2 100644
--- a/arch/powerpc/kernel/perf_event.c
+++ b/arch/powerpc/kernel/perf_event.c
@@ -1220,6 +1220,28 @@ unsigned long perf_instruction_pointer(struct pt_regs *regs)
return ip;
}

+static bool pmc_overflow(unsigned long val)
+{
+ if ((int)val < 0)
+ return true;
+
+ /*
+ * Events on POWER7 can roll back if a speculative event doesn't
+ * eventually complete. Unfortunately in some rare cases they will
+ * raise a performance monitor exception. We need to catch this to
+ * ensure we reset the PMC. In all cases the PMC will be 256 or less
+ * cycles from overflow.
+ *
+ * We only do this if the first pass fails to find any overflowing
+ * PMCs because a user might set a period of less than 256 and we
+ * don't want to mistakenly reset them.
+ */
+ if (__is_processor(PV_POWER7) && ((0x80000000 - val) <= 256))
+ return true;
+
+ return false;
+}
+
/*
* Performance monitor interrupt stuff
*/
@@ -1267,7 +1289,7 @@ static void perf_event_interrupt(struct pt_regs *regs)
if (is_limited_pmc(i + 1))
continue;
val = read_pmc(i + 1);
- if ((int)val < 0)
+ if (pmc_overflow(val))
write_pmc(i + 1, 0);
}
}
--
1.7.4.4