From 813312110bede27bffd082c25cd31730bd567beb Mon Sep 17 00:00:00 2001 From: Sukadev Bhattiprolu Date: Tue, 7 Aug 2012 15:07:19 +0000 Subject: [PATCH] powerpc/perf: Use pmc_overflow() to detect rolled back events For certain speculative events on Power7, 'perf stat' reports far higher event count than 'perf record' for the same event. As described in following commit, a performance monitor exception is raised even when the the performance events are rolled back. commit 0837e3242c73566fc1c0196b4ec61779c25ffc93 Author: Anton Blanchard Date: Wed Mar 9 14:38:42 2011 +1100 perf_event_interrupt() records an event only when an overflow occurs. But this check for overflow is a simple 'if (val < 0)'. Because the events are rolled back, this check for overflow fails and the event is not recorded. perf_event_interrupt() later uses pmc_overflow() to detect the overflow and resets the counters and the events are lost completely. To properly detect the overflow of rolled back events, use pmc_overflow() even when recording events. To reproduce: $ cat strcpy.c #include #include main() { char buf[256]; alarm(5); while(1) strcpy(buf, "string1"); } $ perf record -e r20014 ./strcpy $ perf report -n > report.1 $ perf stat -e r20014 > report.2 # Compare report.1 and report.2 Reported-by: Maynard Johnson Signed-off-by: Sukadev Bhattiprolu Signed-off-by: Benjamin Herrenschmidt --- arch/powerpc/perf/core-book3s.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c index 77b49ddda9d3..7cd2dbd6e4c4 100644 --- a/arch/powerpc/perf/core-book3s.c +++ b/arch/powerpc/perf/core-book3s.c @@ -1431,7 +1431,7 @@ static void perf_event_interrupt(struct pt_regs *regs) if (!event->hw.idx || is_limited_pmc(event->hw.idx)) continue; val = read_pmc(event->hw.idx); - if ((int)val < 0) { + if (pmc_overflow(val)) { /* event has overflowed */ found = 1; record_and_restart(event, val, regs); -- 2.34.1