Messages in this thread Patch in this message | | | Date | Mon, 27 Feb 2012 17:02:09 -0800 | From | Greg KH <> | Subject | [ 06/73] powerpc/perf: power_pmu_start restores incorrect values, breaking frequency events |
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3.0-stable review patch. If anyone has any objections, please let me know.
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From: Anton Blanchard <anton@samba.org>
commit 9a45a9407c69d068500923480884661e2b9cc421 upstream.
perf on POWER stopped working after commit e050e3f0a71b (perf: Fix broken interrupt rate throttling). That patch exposed a bug in the POWER perf_events code.
Since the PMCs count upwards and take an exception when the top bit is set, we want to write 0x80000000 - left in power_pmu_start. We were instead programming in left which effectively disables the counter until we eventually hit 0x80000000. This could take seconds or longer.
With the patch applied I get the expected number of samples:
SAMPLE events: 9948
Signed-off-by: Anton Blanchard <anton@samba.org> Acked-by: Paul Mackerras <paulus@samba.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- arch/powerpc/kernel/perf_event.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
--- a/arch/powerpc/kernel/perf_event.c +++ b/arch/powerpc/kernel/perf_event.c @@ -865,6 +865,7 @@ static void power_pmu_start(struct perf_ { unsigned long flags; s64 left; + unsigned long val; if (!event->hw.idx || !event->hw.sample_period) return; @@ -880,7 +881,12 @@ static void power_pmu_start(struct perf_ event->hw.state = 0; left = local64_read(&event->hw.period_left); - write_pmc(event->hw.idx, left); + + val = 0; + if (left < 0x80000000L) + val = 0x80000000L - left; + + write_pmc(event->hw.idx, val); perf_event_update_userpage(event); perf_pmu_enable(event->pmu);
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