lkml.org 
[lkml]   [2012]   [Feb]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    Subject[ 06/73] powerpc/perf: power_pmu_start restores incorrect values, breaking frequency events
    3.0-stable review patch.  If anyone has any objections, please let me know.

    ------------------
    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);



    \
     
     \ /
      Last update: 2012-02-28 02:39    [from the cache]
    ©2003-2011 Jasper Spaans