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    SubjectRe: [PATCH 1/3] perf, x86: Fix accidentally ack'ing a second event on intel perf counter
    On Thu, Sep 02, 2010 at 04:00:21PM -0400, Don Zickus wrote:
    > On Thu, Sep 02, 2010 at 11:26:27PM +0400, Cyrill Gorcunov wrote:
    > > Lets assume 1 counters is triggered and global bit is set as well
    > >
    > > we have here
    > >
    > > status = intel_pmu_get_status();
    > >
    > > > perf_sample_data_init(&data, 0);
    > > >
    > > > @@ -728,6 +728,7 @@ static int intel_pmu_handle_irq(struct pt_regs *regs)
    > > >
    > > > loops = 0;
    > > > again:
    > > > + intel_pmu_ack_status(status);
    > >
    > > So here we write just being read value back to CTRL register and _if_ new
    > > overflow happened in this window we've cleared it without processing.
    >
    > No, you have to write a '1' to clear. If a new bit is set after we read
    > it, then our 'status' var should have a '0' in that bit and thus will not
    > get cleared when we ack it.
    >

    Yeah, messed {0;1} values, thanks!

    > Cheers,
    > Don
    >
    -- Cyrill


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