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 <an...@samba.org>
Cc: sta...@kernel.org
---
I would prefer not to add the PVR check, but I think we want to limit
this workaround to POWER7. Would a cpu feature be preferable?
Index: linux-2.6/arch/powerpc/kernel/perf_event.c
===================================================================
--- linux-2.6.orig/arch/powerpc/kernel/perf_event.c 2011-03-08
20:11:38.029800971 +1100
+++ linux-2.6/arch/powerpc/kernel/perf_event.c 2011-03-09 14:19:18.756143799
+1100
@@ -1269,6 +1269,28 @@ unsigned long perf_instruction_pointer(s
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
*/
@@ -1316,7 +1338,7 @@ static void perf_event_interrupt(struct
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);
}
}
Index: linux-2.6/arch/powerpc/include/asm/reg.h
===================================================================
--- linux-2.6.orig/arch/powerpc/include/asm/reg.h 2011-03-08
20:11:38.019800609 +1100
+++ linux-2.6/arch/powerpc/include/asm/reg.h 2011-03-09 14:13:56.674461835
+1100
@@ -880,6 +880,7 @@
#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
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