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    SubjectRe: perf hw in kexeced kernel broken in tip
    On 12/07/2010 01:16 PM, Don Zickus wrote:
    > On Thu, Dec 02, 2010 at 08:34:30AM +0100, Peter Zijlstra wrote:
    >>> void __init lockup_detector_init(void)
    >>> {
    >>> void *cpu = (void *)(long)smp_processor_id();
    >>> @@ -563,6 +576,7 @@ void __init lockup_detector_init(void)
    >>>
    >>> cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
    >>> register_cpu_notifier(&cpu_nfb);
    >>> + register_reboot_notifier(&reboot_nfb);
    >>>
    >>> return;
    >>> }
    >>
    >> We'd really want a perf_event.c callback there to do as the hot-unplug
    >> code does and detach all running counters from the cpu.
    >
    > Ok, here is a simpler patch for now.
    >
    > --------------------------------8<--------
    > From: Don Zickus <dzickus@redhat.com>
    > Date: Tue, 7 Dec 2010 16:06:59 -0500
    > Subject: [PATCH] perf: Use event select bits for hardware check
    >
    > The counter registers can continue to increment if left enabled
    > across a kexec or a kdump. The makes the perf hardware check
    > accidentally return false when the hardware really does exist.
    >
    > Change the check to use the first bits of event selection. Those
    > bits should be safe as they are used to program the type of events
    > to use. And more importantly, they won't increment across kexec/kdump.
    >
    > Signed-off-by: Don Zickus <dzickus@redhat.com>
    > ---
    > arch/x86/kernel/cpu/perf_event.c | 8 ++++----
    > 1 files changed, 4 insertions(+), 4 deletions(-)
    >
    > diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
    > index 7b91396..7d869c0 100644
    > --- a/arch/x86/kernel/cpu/perf_event.c
    > +++ b/arch/x86/kernel/cpu/perf_event.c
    > @@ -377,10 +377,10 @@ static bool check_hw_exists(void)
    > u64 val, val_new = 0;
    > int ret = 0;
    >
    > - val = 0xabcdUL;
    > - ret |= checking_wrmsrl(x86_pmu.perfctr, val);
    > - ret |= rdmsrl_safe(x86_pmu.perfctr, &val_new);
    > - if (ret || val != val_new)
    > + val = 0xabUL;
    > + ret |= checking_wrmsrl(x86_pmu.eventsel, val);
    > + ret |= rdmsrl_safe(x86_pmu.eventsel, &val_new);
    > + if (ret || val != (val_new & 0xFF))
    > return false;
    >
    > return true;

    Thanks. it fixes the problem.

    Yinghai


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