perf, powerpc: Handle events that raise an exception without overflowing

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: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index bc8dd53f718a1b201a16e91f4864bb221f5acb25..6f6bd54e8b08cb7a4f9ab4c96ddf6137f2fa326f 100644 (file)
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -860,6 +860,7 @@
 #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 a3c0a32c4628697c8d4b2311355700121541da83..8291a3cf7056ee54ac84da593c365140d81dccc7 100644 (file)
--- 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);
                }
        }