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    Subject[tip:perfcounters/core] perf_counter: pmc arbitration
    Commit-ID:  b4110aa4b80378855c92a090dc079a3c5c69b69c
    Gitweb: http://git.kernel.org/tip/b4110aa4b80378855c92a090dc079a3c5c69b69c
    Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
    AuthorDate: Mon, 30 Mar 2009 19:07:16 +0200
    Committer: Ingo Molnar <mingo@elte.hu>
    CommitDate: Wed, 1 Apr 2009 11:33:39 +0200

    perf_counter: pmc arbitration

    Follow the example set by powerpc and try to play nice with oprofile
    and the nmi watchdog.

    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Acked-by: Paul Mackerras <paulus@samba.org>
    LKML-Reference: <20090330171024.459968444@chello.nl>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>


    ---
    arch/x86/kernel/cpu/perf_counter.c | 75 ++++++++++++++++++++++++++++++++++++
    1 files changed, 75 insertions(+), 0 deletions(-)

    diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c
    index e16dfaf..2a946a1 100644
    --- a/arch/x86/kernel/cpu/perf_counter.c
    +++ b/arch/x86/kernel/cpu/perf_counter.c
    @@ -20,6 +20,7 @@

    #include <asm/apic.h>
    #include <asm/stacktrace.h>
    +#include <asm/nmi.h>

    static bool perf_counters_initialized __read_mostly;

    @@ -172,6 +173,65 @@ again:
    atomic64_sub(delta, &hwc->period_left);
    }

    +static atomic_t num_counters;
    +static DEFINE_MUTEX(pmc_reserve_mutex);
    +
    +static bool reserve_pmc_hardware(void)
    +{
    + int i;
    +
    + if (nmi_watchdog == NMI_LOCAL_APIC)
    + disable_lapic_nmi_watchdog();
    +
    + for (i = 0; i < nr_counters_generic; i++) {
    + if (!reserve_perfctr_nmi(pmc_ops->perfctr + i))
    + goto perfctr_fail;
    + }
    +
    + for (i = 0; i < nr_counters_generic; i++) {
    + if (!reserve_evntsel_nmi(pmc_ops->eventsel + i))
    + goto eventsel_fail;
    + }
    +
    + return true;
    +
    +eventsel_fail:
    + for (i--; i >= 0; i--)
    + release_evntsel_nmi(pmc_ops->eventsel + i);
    +
    + i = nr_counters_generic;
    +
    +perfctr_fail:
    + for (i--; i >= 0; i--)
    + release_perfctr_nmi(pmc_ops->perfctr + i);
    +
    + if (nmi_watchdog == NMI_LOCAL_APIC)
    + enable_lapic_nmi_watchdog();
    +
    + return false;
    +}
    +
    +static void release_pmc_hardware(void)
    +{
    + int i;
    +
    + for (i = 0; i < nr_counters_generic; i++) {
    + release_perfctr_nmi(pmc_ops->perfctr + i);
    + release_evntsel_nmi(pmc_ops->eventsel + i);
    + }
    +
    + if (nmi_watchdog == NMI_LOCAL_APIC)
    + enable_lapic_nmi_watchdog();
    +}
    +
    +static void hw_perf_counter_destroy(struct perf_counter *counter)
    +{
    + if (atomic_dec_and_mutex_lock(&num_counters, &pmc_reserve_mutex)) {
    + release_pmc_hardware();
    + mutex_unlock(&pmc_reserve_mutex);
    + }
    +}
    +
    /*
    * Setup the hardware configuration for a given hw_event_type
    */
    @@ -179,10 +239,23 @@ static int __hw_perf_counter_init(struct perf_counter *counter)
    {
    struct perf_counter_hw_event *hw_event = &counter->hw_event;
    struct hw_perf_counter *hwc = &counter->hw;
    + int err;

    if (unlikely(!perf_counters_initialized))
    return -EINVAL;

    + err = 0;
    + if (atomic_inc_not_zero(&num_counters)) {
    + mutex_lock(&pmc_reserve_mutex);
    + if (atomic_read(&num_counters) == 0 && !reserve_pmc_hardware())
    + err = -EBUSY;
    + else
    + atomic_inc(&num_counters);
    + mutex_unlock(&pmc_reserve_mutex);
    + }
    + if (err)
    + return err;
    +
    /*
    * Generate PMC IRQs:
    * (keep 'enabled' bit clear for now)
    @@ -230,6 +303,8 @@ static int __hw_perf_counter_init(struct perf_counter *counter)
    hwc->config |= pmc_ops->event_map(perf_event_id(hw_event));
    }

    + counter->destroy = hw_perf_counter_destroy;
    +
    return 0;
    }


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