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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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