From 0837e3242c73566fc1c0196b4ec61779c25ffc93 Mon Sep 17 00:00:00 2001 From: Anton Blanchard Date: Wed, 9 Mar 2011 14:38:42 +1100 Subject: 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 Signed-off-by: Peter Zijlstra Cc: # as far back as it applies cleanly LKML-Reference: <20110309143842.6c22845e@kryten> Signed-off-by: Ingo Molnar --- arch/powerpc/kernel/perf_event.c | 24 +++++++++++++++++++++++- 1 file changed, 23 insertions(+), 1 deletion(-) (limited to 'arch/powerpc/kernel/perf_event.c') diff --git a/arch/powerpc/kernel/perf_event.c b/arch/powerpc/kernel/perf_event.c index ab6f6beadb57..97e0ae414940 100644 --- a/arch/powerpc/kernel/perf_event.c +++ b/arch/powerpc/kernel/perf_event.c @@ -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); } } -- cgit v1.2.3