powerpc/perf_counter: Add generic support for POWER-family PMU hardware

This provides the architecture-specific functions needed to access
PMU hardware on the 64-bit PowerPC processors.  It has been designed
for the IBM POWER family (POWER 4/4+/5/5+/6 and PPC970) but will
hopefully also suit other 64-bit PowerPC machines (although probably
not Cell given how different it is in this area).  This doesn't
include back-ends for any specific processors.

This implements a system which allows back-ends to express the
constraints that their hardware has on what events can be counted
simultaneously.  The constraints are expressed as a 64-bit mask +
64-bit value for each event, and the encoding is capable of
expressing the constraints arising from having a set of multiplexers
feeding an event bus, with some events being available through
multiple multiplexer settings, such as we get on POWER4 and PPC970.
Furthermore, the back-end can supply alternative event codes for
each event, and the constraint checking code will try all possible
combinations of alternative event codes to try to find a combination
that will fit.

Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 754 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/perf_counter.c b/arch/powerpc/kernel/perf_counter.c
new file mode 100644
index 000000000000..c7d4c2966a5c
--- /dev/null
+++ b/arch/powerpc/kernel/perf_counter.c
@@ -0,0 +1,754 @@
+/*
+ * Performance counter support - powerpc architecture code
+ *
+ * Copyright 2008-2009 Paul Mackerras, IBM Corporation.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/perf_counter.h>
+#include <linux/percpu.h>
+#include <linux/hardirq.h>
+#include <asm/reg.h>
+#include <asm/pmc.h>
+
+struct cpu_hw_counters {
+        int n_counters;
+        int n_percpu;
+        int disabled;
+        int n_added;
+        struct perf_counter *counter[MAX_HWCOUNTERS];
+        unsigned int events[MAX_HWCOUNTERS];
+        u64 mmcr[3];
+};
+DEFINE_PER_CPU(struct cpu_hw_counters, cpu_hw_counters);
+
+struct power_pmu *ppmu;
+
+void perf_counter_print_debug(void)
+{
+}
+
+/*
+ * Return 1 for a software counter, 0 for a hardware counter
+ */
+static inline int is_software_counter(struct perf_counter *counter)
+{
+        return !counter->hw_event.raw && counter->hw_event.type < 0;
+}
+
+/*
+ * Read one performance monitor counter (PMC).
+ */
+static unsigned long read_pmc(int idx)
+{
+        unsigned long val;
+
+        switch (idx) {
+        case 1:
+                val = mfspr(SPRN_PMC1);
+                break;
+        case 2:
+                val = mfspr(SPRN_PMC2);
+                break;
+        case 3:
+                val = mfspr(SPRN_PMC3);
+                break;
+        case 4:
+                val = mfspr(SPRN_PMC4);
+                break;
+        case 5:
+                val = mfspr(SPRN_PMC5);
+                break;
+        case 6:
+                val = mfspr(SPRN_PMC6);
+                break;
+        case 7:
+                val = mfspr(SPRN_PMC7);
+                break;
+        case 8:
+                val = mfspr(SPRN_PMC8);
+                break;
+        default:
+                printk(KERN_ERR "oops trying to read PMC%d\n", idx);
+                val = 0;
+        }
+        return val;
+}
+
+/*
+ * Write one PMC.
+ */
+static void write_pmc(int idx, unsigned long val)
+{
+        switch (idx) {
+        case 1:
+                mtspr(SPRN_PMC1, val);
+                break;
+        case 2:
+                mtspr(SPRN_PMC2, val);
+                break;
+        case 3:
+                mtspr(SPRN_PMC3, val);
+                break;
+        case 4:
+                mtspr(SPRN_PMC4, val);
+                break;
+        case 5:
+                mtspr(SPRN_PMC5, val);
+                break;
+        case 6:
+                mtspr(SPRN_PMC6, val);
+                break;
+        case 7:
+                mtspr(SPRN_PMC7, val);
+                break;
+        case 8:
+                mtspr(SPRN_PMC8, val);
+                break;
+        default:
+                printk(KERN_ERR "oops trying to write PMC%d\n", idx);
+        }
+}
+
+/*
+ * Check if a set of events can all go on the PMU at once.
+ * If they can't, this will look at alternative codes for the events
+ * and see if any combination of alternative codes is feasible.
+ * The feasible set is returned in event[].
+ */
+static int power_check_constraints(unsigned int event[], int n_ev)
+{
+        u64 mask, value, nv;
+        unsigned int alternatives[MAX_HWCOUNTERS][MAX_EVENT_ALTERNATIVES];
+        u64 amasks[MAX_HWCOUNTERS][MAX_EVENT_ALTERNATIVES];
+        u64 avalues[MAX_HWCOUNTERS][MAX_EVENT_ALTERNATIVES];
+        u64 smasks[MAX_HWCOUNTERS], svalues[MAX_HWCOUNTERS];
+        int n_alt[MAX_HWCOUNTERS], choice[MAX_HWCOUNTERS];
+        int i, j;
+        u64 addf = ppmu->add_fields;
+        u64 tadd = ppmu->test_adder;
+
+        if (n_ev > ppmu->n_counter)
+                return -1;
+
+        /* First see if the events will go on as-is */
+        for (i = 0; i < n_ev; ++i) {
+                alternatives[i][0] = event[i];
+                if (ppmu->get_constraint(event[i], &amasks[i][0],
+                                         &avalues[i][0]))
+                        return -1;
+                choice[i] = 0;
+        }
+        value = mask = 0;
+        for (i = 0; i < n_ev; ++i) {
+                nv = (value | avalues[i][0]) + (value & avalues[i][0] & addf);
+                if ((((nv + tadd) ^ value) & mask) != 0 ||
+                    (((nv + tadd) ^ avalues[i][0]) & amasks[i][0]) != 0)
+                        break;
+                value = nv;
+                mask |= amasks[i][0];
+        }
+        if (i == n_ev)
+                return 0;       /* all OK */
+
+        /* doesn't work, gather alternatives... */
+        if (!ppmu->get_alternatives)
+                return -1;
+        for (i = 0; i < n_ev; ++i) {
+                n_alt[i] = ppmu->get_alternatives(event[i], alternatives[i]);
+                for (j = 1; j < n_alt[i]; ++j)
+                        ppmu->get_constraint(alternatives[i][j],
+                                             &amasks[i][j], &avalues[i][j]);
+        }
+
+        /* enumerate all possibilities and see if any will work */
+        i = 0;
+        j = -1;
+        value = mask = nv = 0;
+        while (i < n_ev) {
+                if (j >= 0) {
+                        /* we're backtracking, restore context */
+                        value = svalues[i];
+                        mask = smasks[i];
+                        j = choice[i];
+                }
+                /*
+                 * See if any alternative k for event i,
+                 * where k > j, will satisfy the constraints.
+                 */
+                while (++j < n_alt[i]) {
+                        nv = (value | avalues[i][j]) +
+                                (value & avalues[i][j] & addf);
+                        if ((((nv + tadd) ^ value) & mask) == 0 &&
+                            (((nv + tadd) ^ avalues[i][j])
+                             & amasks[i][j]) == 0)
+                                break;
+                }
+                if (j >= n_alt[i]) {
+                        /*
+                         * No feasible alternative, backtrack
+                         * to event i-1 and continue enumerating its
+                         * alternatives from where we got up to.
+                         */
+                        if (--i < 0)
+                                return -1;
+                } else {
+                        /*
+                         * Found a feasible alternative for event i,
+                         * remember where we got up to with this event,
+                         * go on to the next event, and start with
+                         * the first alternative for it.
+                         */
+                        choice[i] = j;
+                        svalues[i] = value;
+                        smasks[i] = mask;
+                        value = nv;
+                        mask |= amasks[i][j];
+                        ++i;
+                        j = -1;
+                }
+        }
+
+        /* OK, we have a feasible combination, tell the caller the solution */
+        for (i = 0; i < n_ev; ++i)
+                event[i] = alternatives[i][choice[i]];
+        return 0;
+}
+
+static void power_perf_read(struct perf_counter *counter)
+{
+        long val, delta, prev;
+
+        if (!counter->hw.idx)
+                return;
+        /*
+         * Performance monitor interrupts come even when interrupts
+         * are soft-disabled, as long as interrupts are hard-enabled.
+         * Therefore we treat them like NMIs.
+         */
+        do {
+                prev = atomic64_read(&counter->hw.prev_count);
+                barrier();
+                val = read_pmc(counter->hw.idx);
+        } while (atomic64_cmpxchg(&counter->hw.prev_count, prev, val) != prev);
+
+        /* The counters are only 32 bits wide */
+        delta = (val - prev) & 0xfffffffful;
+        atomic64_add(delta, &counter->count);
+        atomic64_sub(delta, &counter->hw.period_left);
+}
+
+/*
+ * Disable all counters to prevent PMU interrupts and to allow
+ * counters to be added or removed.
+ */
+u64 hw_perf_save_disable(void)
+{
+        struct cpu_hw_counters *cpuhw;
+        unsigned long ret;
+        unsigned long flags;
+
+        local_irq_save(flags);
+        cpuhw = &__get_cpu_var(cpu_hw_counters);
+
+        ret = cpuhw->disabled;
+        if (!ret) {
+                cpuhw->disabled = 1;
+                cpuhw->n_added = 0;
+
+                /*
+                 * Set the 'freeze counters' bit.
+                 * The barrier is to make sure the mtspr has been
+                 * executed and the PMU has frozen the counters
+                 * before we return.
+                 */
+                mtspr(SPRN_MMCR0, mfspr(SPRN_MMCR0) | MMCR0_FC);
+                mb();
+        }
+        local_irq_restore(flags);
+        return ret;
+}
+
+/*
+ * Re-enable all counters if disable == 0.
+ * If we were previously disabled and counters were added, then
+ * put the new config on the PMU.
+ */
+void hw_perf_restore(u64 disable)
+{
+        struct perf_counter *counter;
+        struct cpu_hw_counters *cpuhw;
+        unsigned long flags;
+        long i;
+        unsigned long val;
+        s64 left;
+        unsigned int hwc_index[MAX_HWCOUNTERS];
+
+        if (disable)
+                return;
+        local_irq_save(flags);
+        cpuhw = &__get_cpu_var(cpu_hw_counters);
+        cpuhw->disabled = 0;
+
+        /*
+         * If we didn't change anything, or only removed counters,
+         * no need to recalculate MMCR* settings and reset the PMCs.
+         * Just reenable the PMU with the current MMCR* settings
+         * (possibly updated for removal of counters).
+         */
+        if (!cpuhw->n_added) {
+                mtspr(SPRN_MMCRA, cpuhw->mmcr[2]);
+                mtspr(SPRN_MMCR1, cpuhw->mmcr[1]);
+                mtspr(SPRN_MMCR0, cpuhw->mmcr[0]);
+                goto out;
+        }
+
+        /*
+         * Compute MMCR* values for the new set of counters
+         */
+        if (ppmu->compute_mmcr(cpuhw->events, cpuhw->n_counters, hwc_index,
+                               cpuhw->mmcr)) {
+                /* shouldn't ever get here */
+                printk(KERN_ERR "oops compute_mmcr failed\n");
+                goto out;
+        }
+
+        /*
+         * Write the new configuration to MMCR* with the freeze
+         * bit set and set the hardware counters to their initial values.
+         * Then unfreeze the counters.
+         */
+        mtspr(SPRN_MMCRA, cpuhw->mmcr[2]);
+        mtspr(SPRN_MMCR1, cpuhw->mmcr[1]);
+        mtspr(SPRN_MMCR0, (cpuhw->mmcr[0] & ~(MMCR0_PMC1CE | MMCR0_PMCjCE))
+                                | MMCR0_FC);
+
+        /*
+         * Read off any pre-existing counters that need to move
+         * to another PMC.
+         */
+        for (i = 0; i < cpuhw->n_counters; ++i) {
+                counter = cpuhw->counter[i];
+                if (counter->hw.idx && counter->hw.idx != hwc_index[i] + 1) {
+                        power_perf_read(counter);
+                        write_pmc(counter->hw.idx, 0);
+                        counter->hw.idx = 0;
+                }
+        }
+
+        /*
+         * Initialize the PMCs for all the new and moved counters.
+         */
+        for (i = 0; i < cpuhw->n_counters; ++i) {
+                counter = cpuhw->counter[i];
+                if (counter->hw.idx)
+                        continue;
+                val = 0;
+                if (counter->hw_event.irq_period) {
+                        left = atomic64_read(&counter->hw.period_left);
+                        if (left < 0x80000000L)
+                                val = 0x80000000L - left;
+                }
+                atomic64_set(&counter->hw.prev_count, val);
+                counter->hw.idx = hwc_index[i] + 1;
+                write_pmc(counter->hw.idx, val);
+        }
+        mb();
+        cpuhw->mmcr[0] |= MMCR0_PMXE | MMCR0_FCECE;
+        mtspr(SPRN_MMCR0, cpuhw->mmcr[0]);
+
+ out:
+        local_irq_restore(flags);
+}
+
+static int collect_events(struct perf_counter *group, int max_count,
+                          struct perf_counter *ctrs[], unsigned int *events)
+{
+        int n = 0;
+        struct perf_counter *counter;
+
+        if (!is_software_counter(group)) {
+                if (n >= max_count)
+                        return -1;
+                ctrs[n] = group;
+                events[n++] = group->hw.config;
+        }
+        list_for_each_entry(counter, &group->sibling_list, list_entry) {
+                if (!is_software_counter(counter) &&
+                    counter->state != PERF_COUNTER_STATE_OFF) {
+                        if (n >= max_count)
+                                return -1;
+                        ctrs[n] = counter;
+                        events[n++] = counter->hw.config;
+                }
+        }
+        return n;
+}
+
+static void counter_sched_in(struct perf_counter *counter, int cpu)
+{
+        counter->state = PERF_COUNTER_STATE_ACTIVE;
+        counter->oncpu = cpu;
+        if (is_software_counter(counter))
+                counter->hw_ops->enable(counter);
+}
+
+/*
+ * Called to enable a whole group of counters.
+ * Returns 1 if the group was enabled, or -EAGAIN if it could not be.
+ * Assumes the caller has disabled interrupts and has
+ * frozen the PMU with hw_perf_save_disable.
+ */
+int hw_perf_group_sched_in(struct perf_counter *group_leader,
+               struct perf_cpu_context *cpuctx,
+               struct perf_counter_context *ctx, int cpu)
+{
+        struct cpu_hw_counters *cpuhw;
+        long i, n, n0;
+        struct perf_counter *sub;
+
+        cpuhw = &__get_cpu_var(cpu_hw_counters);
+        n0 = cpuhw->n_counters;
+        n = collect_events(group_leader, ppmu->n_counter - n0,
+                           &cpuhw->counter[n0], &cpuhw->events[n0]);
+        if (n < 0)
+                return -EAGAIN;
+        if (power_check_constraints(cpuhw->events, n + n0))
+                return -EAGAIN;
+        cpuhw->n_counters = n0 + n;
+        cpuhw->n_added += n;
+
+        /*
+         * OK, this group can go on; update counter states etc.,
+         * and enable any software counters
+         */
+        for (i = n0; i < n0 + n; ++i)
+                cpuhw->counter[i]->hw.config = cpuhw->events[i];
+        n = 1;
+        counter_sched_in(group_leader, cpu);
+        list_for_each_entry(sub, &group_leader->sibling_list, list_entry) {
+                if (sub->state != PERF_COUNTER_STATE_OFF) {
+                        counter_sched_in(sub, cpu);
+                        ++n;
+                }
+        }
+        cpuctx->active_oncpu += n;
+        ctx->nr_active += n;
+
+        return 1;
+}
+
+/*
+ * Add a counter to the PMU.
+ * If all counters are not already frozen, then we disable and
+ * re-enable the PMU in order to get hw_perf_restore to do the
+ * actual work of reconfiguring the PMU.
+ */
+static int power_perf_enable(struct perf_counter *counter)
+{
+        struct cpu_hw_counters *cpuhw;
+        unsigned long flags;
+        u64 pmudis;
+        int n0;
+        int ret = -EAGAIN;
+
+        local_irq_save(flags);
+        pmudis = hw_perf_save_disable();
+
+        /*
+         * Add the counter to the list (if there is room)
+         * and check whether the total set is still feasible.
+         */
+        cpuhw = &__get_cpu_var(cpu_hw_counters);
+        n0 = cpuhw->n_counters;
+        if (n0 >= ppmu->n_counter)
+                goto out;
+        cpuhw->counter[n0] = counter;
+        cpuhw->events[n0] = counter->hw.config;
+        if (power_check_constraints(cpuhw->events, n0 + 1))
+                goto out;
+
+        counter->hw.config = cpuhw->events[n0];
+        ++cpuhw->n_counters;
+        ++cpuhw->n_added;
+
+        ret = 0;
+ out:
+        hw_perf_restore(pmudis);
+        local_irq_restore(flags);
+        return ret;
+}
+
+/*
+ * Remove a counter from the PMU.
+ */
+static void power_perf_disable(struct perf_counter *counter)
+{
+        struct cpu_hw_counters *cpuhw;
+        long i;
+        u64 pmudis;
+        unsigned long flags;
+
+        local_irq_save(flags);
+        pmudis = hw_perf_save_disable();
+
+        power_perf_read(counter);
+
+        cpuhw = &__get_cpu_var(cpu_hw_counters);
+        for (i = 0; i < cpuhw->n_counters; ++i) {
+                if (counter == cpuhw->counter[i]) {
+                        while (++i < cpuhw->n_counters)
+                                cpuhw->counter[i-1] = cpuhw->counter[i];
+                        --cpuhw->n_counters;
+                        ppmu->disable_pmc(counter->hw.idx - 1, cpuhw->mmcr);
+                        write_pmc(counter->hw.idx, 0);
+                        counter->hw.idx = 0;
+                        break;
+                }
+        }
+        if (cpuhw->n_counters == 0) {
+                /* disable exceptions if no counters are running */
+                cpuhw->mmcr[0] &= ~(MMCR0_PMXE | MMCR0_FCECE);
+        }
+
+        hw_perf_restore(pmudis);
+        local_irq_restore(flags);
+}
+
+struct hw_perf_counter_ops power_perf_ops = {
+        .enable = power_perf_enable,
+        .disable = power_perf_disable,
+        .read = power_perf_read
+};
+
+const struct hw_perf_counter_ops *
+hw_perf_counter_init(struct perf_counter *counter)
+{
+        unsigned long ev;
+        struct perf_counter *ctrs[MAX_HWCOUNTERS];
+        unsigned int events[MAX_HWCOUNTERS];
+        int n;
+
+        if (!ppmu)
+                return NULL;
+        if ((s64)counter->hw_event.irq_period < 0)
+                return NULL;
+        ev = counter->hw_event.type;
+        if (!counter->hw_event.raw) {
+                if (ev >= ppmu->n_generic ||
+                    ppmu->generic_events[ev] == 0)
+                        return NULL;
+                ev = ppmu->generic_events[ev];
+        }
+        counter->hw.config_base = ev;
+        counter->hw.idx = 0;
+
+        /*
+         * If this is in a group, check if it can go on with all the
+         * other hardware counters in the group.  We assume the counter
+         * hasn't been linked into its leader's sibling list at this point.
+         */
+        n = 0;
+        if (counter->group_leader != counter) {
+                n = collect_events(counter->group_leader, ppmu->n_counter - 1,
+                                   ctrs, events);
+                if (n < 0)
+                        return NULL;
+        }
+        events[n++] = ev;
+        if (power_check_constraints(events, n))
+                return NULL;
+
+        counter->hw.config = events[n - 1];
+        atomic64_set(&counter->hw.period_left, counter->hw_event.irq_period);
+        return &power_perf_ops;
+}
+
+/*
+ * Handle wakeups.
+ */
+void perf_counter_do_pending(void)
+{
+        int i;
+        struct cpu_hw_counters *cpuhw = &__get_cpu_var(cpu_hw_counters);
+        struct perf_counter *counter;
+
+        set_perf_counter_pending(0);
+        for (i = 0; i < cpuhw->n_counters; ++i) {
+                counter = cpuhw->counter[i];
+                if (counter && counter->wakeup_pending) {
+                        counter->wakeup_pending = 0;
+                        wake_up(&counter->waitq);
+                }
+        }
+}
+
+/*
+ * Record data for an irq counter.
+ * This function was lifted from the x86 code; maybe it should
+ * go in the core?
+ */
+static void perf_store_irq_data(struct perf_counter *counter, u64 data)
+{
+        struct perf_data *irqdata = counter->irqdata;
+
+        if (irqdata->len > PERF_DATA_BUFLEN - sizeof(u64)) {
+                irqdata->overrun++;
+        } else {
+                u64 *p = (u64 *) &irqdata->data[irqdata->len];
+
+                *p = data;
+                irqdata->len += sizeof(u64);
+        }
+}
+
+/*
+ * Record all the values of the counters in a group
+ */
+static void perf_handle_group(struct perf_counter *counter)
+{
+        struct perf_counter *leader, *sub;
+
+        leader = counter->group_leader;
+        list_for_each_entry(sub, &leader->sibling_list, list_entry) {
+                if (sub != counter)
+                        sub->hw_ops->read(sub);
+                perf_store_irq_data(counter, sub->hw_event.type);
+                perf_store_irq_data(counter, atomic64_read(&sub->count));
+        }
+}
+
+/*
+ * A counter has overflowed; update its count and record
+ * things if requested.  Note that interrupts are hard-disabled
+ * here so there is no possibility of being interrupted.
+ */
+static void record_and_restart(struct perf_counter *counter, long val,
+                               struct pt_regs *regs)
+{
+        s64 prev, delta, left;
+        int record = 0;
+
+        /* we don't have to worry about interrupts here */
+        prev = atomic64_read(&counter->hw.prev_count);
+        delta = (val - prev) & 0xfffffffful;
+        atomic64_add(delta, &counter->count);
+
+        /*
+         * See if the total period for this counter has expired,
+         * and update for the next period.
+         */
+        val = 0;
+        left = atomic64_read(&counter->hw.period_left) - delta;
+        if (counter->hw_event.irq_period) {
+                if (left <= 0) {
+                        left += counter->hw_event.irq_period;
+                        if (left <= 0)
+                                left = counter->hw_event.irq_period;
+                        record = 1;
+                }
+                if (left < 0x80000000L)
+                        val = 0x80000000L - left;
+        }
+        write_pmc(counter->hw.idx, val);
+        atomic64_set(&counter->hw.prev_count, val);
+        atomic64_set(&counter->hw.period_left, left);
+
+        /*
+         * Finally record data if requested.
+         */
+        if (record) {
+                switch (counter->hw_event.record_type) {
+                case PERF_RECORD_SIMPLE:
+                        break;
+                case PERF_RECORD_IRQ:
+                        perf_store_irq_data(counter, instruction_pointer(regs));
+                        counter->wakeup_pending = 1;
+                        break;
+                case PERF_RECORD_GROUP:
+                        perf_handle_group(counter);
+                        counter->wakeup_pending = 1;
+                        break;
+                }
+        }
+}
+
+/*
+ * Performance monitor interrupt stuff
+ */
+static void perf_counter_interrupt(struct pt_regs *regs)
+{
+        int i;
+        struct cpu_hw_counters *cpuhw = &__get_cpu_var(cpu_hw_counters);
+        struct perf_counter *counter;
+        long val;
+        int need_wakeup = 0, found = 0;
+
+        for (i = 0; i < cpuhw->n_counters; ++i) {
+                counter = cpuhw->counter[i];
+                val = read_pmc(counter->hw.idx);
+                if ((int)val < 0) {
+                        /* counter has overflowed */
+                        found = 1;
+                        record_and_restart(counter, val, regs);
+                        if (counter->wakeup_pending)
+                                need_wakeup = 1;
+                }
+        }
+
+        /*
+         * In case we didn't find and reset the counter that caused
+         * the interrupt, scan all counters and reset any that are
+         * negative, to avoid getting continual interrupts.
+         * Any that we processed in the previous loop will not be negative.
+         */
+        if (!found) {
+                for (i = 0; i < ppmu->n_counter; ++i) {
+                        val = read_pmc(i + 1);
+                        if ((int)val < 0)
+                                write_pmc(i + 1, 0);
+                }
+        }
+
+        /*
+         * Reset MMCR0 to its normal value.  This will set PMXE and
+         * clear FC (freeze counters) and PMAO (perf mon alert occurred)
+         * and thus allow interrupts to occur again.
+         * XXX might want to use MSR.PM to keep the counters frozen until
+         * we get back out of this interrupt.
+         */
+        mtspr(SPRN_MMCR0, cpuhw->mmcr[0]);
+
+        /*
+         * If we need a wakeup, check whether interrupts were soft-enabled
+         * when we took the interrupt.  If they were, we can wake stuff up
+         * immediately; otherwise we'll have to set a flag and do the
+         * wakeup when interrupts get soft-enabled.
+         */
+        if (need_wakeup) {
+                if (regs->softe) {
+                        irq_enter();
+                        perf_counter_do_pending();
+                        irq_exit();
+                } else {
+                        set_perf_counter_pending(1);
+                }
+        }
+}
+
+static int init_perf_counters(void)
+{
+        if (reserve_pmc_hardware(perf_counter_interrupt)) {
+                printk(KERN_ERR "Couldn't init performance monitor subsystem\n");
+                return -EBUSY;
+        }
+
+        return 0;
+}
+
+arch_initcall(init_perf_counters);