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author | Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com> | 2012-08-07 15:07:19 +0000 |
---|---|---|
committer | Benjamin Herrenschmidt <benh@kernel.crashing.org> | 2012-08-24 20:26:10 +1000 |
commit | 813312110bede27bffd082c25cd31730bd567beb (patch) | |
tree | a647b146b9f6e079e77c28a7775b0320344ea3e5 /arch/powerpc/perf | |
parent | 2fae7cdb60240e2e2d9b378afbf6d9fcce8a3890 (diff) | |
download | linux-813312110bede27bffd082c25cd31730bd567beb.tar.gz linux-813312110bede27bffd082c25cd31730bd567beb.tar.bz2 linux-813312110bede27bffd082c25cd31730bd567beb.zip |
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 <anton@samba.org>
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 <stdio.h>
#include <string.h>
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 <mpjohn@us.ibm.com>
Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Diffstat (limited to 'arch/powerpc/perf')
-rw-r--r-- | arch/powerpc/perf/core-book3s.c | 2 |
1 files changed, 1 insertions, 1 deletions
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); |