Skip to content
Permalink
Browse files

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

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>
Cc: <stable@kernel.org> # as far back as it applies cleanly
LKML-Reference: <20110309143842.6c22845e@kryten>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
  • Loading branch information
antonblanchard authored and Ingo Molnar committed Mar 9, 2011
1 parent 7d5d02d commit 0837e3242c73566fc1c0196b4ec61779c25ffc93
Showing with 24 additions and 1 deletion.
  1. +1 −0 arch/powerpc/include/asm/reg.h
  2. +23 −1 arch/powerpc/kernel/perf_event.c
@@ -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
@@ -1269,6 +1269,28 @@ 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
*/
@@ -1316,7 +1338,7 @@ 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);
}
}

0 comments on commit 0837e32

Please sign in to comment.
You can’t perform that action at this time.