linux-vybrid_public/arch/alpha/kernel/perf_event.c

/*
 * Hardware performance events for the Alpha.
 *
 * We implement HW counts on the EV67 and subsequent CPUs only.
 *
 * (C) 2010 Michael J. Cree
 *
 * Somewhat based on the Sparc code, and to a lesser extent the PowerPC and
 * ARM code, which are copyright by their respective authors.
 */

#include <linux/perf_event.h>
#include <linux/kprobes.h>
#include <linux/kernel.h>
#include <linux/kdebug.h>
#include <linux/mutex.h>

#include <asm/hwrpb.h>
#include <asm/atomic.h>
#include <asm/irq.h>
#include <asm/irq_regs.h>
#include <asm/pal.h>
#include <asm/wrperfmon.h>
#include <asm/hw_irq.h>


/* The maximum number of PMCs on any Alpha CPU whatsoever. */
#define MAX_HWEVENTS 3
#define PMC_NO_INDEX -1

/* For tracking PMCs and the hw events they monitor on each CPU. */
struct cpu_hw_events {
	int			enabled;
	/* Number of events scheduled; also number entries valid in arrays below. */
	int			n_events;
	/* Number events added since last hw_perf_disable(). */
	int			n_added;
	/* Events currently scheduled. */
	struct perf_event	*event[MAX_HWEVENTS];
	/* Event type of each scheduled event. */
	unsigned long		evtype[MAX_HWEVENTS];
	/* Current index of each scheduled event; if not yet determined
	 * contains PMC_NO_INDEX.
	 */
	int			current_idx[MAX_HWEVENTS];
	/* The active PMCs' config for easy use with wrperfmon(). */
	unsigned long		config;
	/* The active counters' indices for easy use with wrperfmon(). */
	unsigned long		idx_mask;
};
DEFINE_PER_CPU(struct cpu_hw_events, cpu_hw_events);



/*
 * A structure to hold the description of the PMCs available on a particular
 * type of Alpha CPU.
 */
struct alpha_pmu_t {
	/* Mapping of the perf system hw event types to indigenous event types */
	const int *event_map;
	/* The number of entries in the event_map */
	int  max_events;
	/* The number of PMCs on this Alpha */
	int  num_pmcs;
	/*
	 * All PMC counters reside in the IBOX register PCTR.  This is the
	 * LSB of the counter.
	 */
	int  pmc_count_shift[MAX_HWEVENTS];
	/*
	 * The mask that isolates the PMC bits when the LSB of the counter
	 * is shifted to bit 0.
	 */
	unsigned long pmc_count_mask[MAX_HWEVENTS];
	/* The maximum period the PMC can count. */
	unsigned long pmc_max_period[MAX_HWEVENTS];
	/*
	 * The maximum value that may be written to the counter due to
	 * hardware restrictions is pmc_max_period - pmc_left.
	 */
	long pmc_left[3];
	 /* Subroutine for allocation of PMCs.  Enforces constraints. */
	int (*check_constraints)(struct perf_event **, unsigned long *, int);
};

/*
 * The Alpha CPU PMU description currently in operation.  This is set during
 * the boot process to the specific CPU of the machine.
 */
static const struct alpha_pmu_t *alpha_pmu;


#define HW_OP_UNSUPPORTED -1

/*
 * The hardware description of the EV67, EV68, EV69, EV7 and EV79 PMUs
 * follow. Since they are identical we refer to them collectively as the
 * EV67 henceforth.
 */

/*
 * EV67 PMC event types
 *
 * There is no one-to-one mapping of the possible hw event types to the
 * actual codes that are used to program the PMCs hence we introduce our
 * own hw event type identifiers.
 */
enum ev67_pmc_event_type {
	EV67_CYCLES = 1,
	EV67_INSTRUCTIONS,
	EV67_BCACHEMISS,
	EV67_MBOXREPLAY,
	EV67_LAST_ET
};
#define EV67_NUM_EVENT_TYPES (EV67_LAST_ET-EV67_CYCLES)


/* Mapping of the hw event types to the perf tool interface */
static const int ev67_perfmon_event_map[] = {
	[PERF_COUNT_HW_CPU_CYCLES]	 = EV67_CYCLES,
	[PERF_COUNT_HW_INSTRUCTIONS]	 = EV67_INSTRUCTIONS,
	[PERF_COUNT_HW_CACHE_REFERENCES] = HW_OP_UNSUPPORTED,
	[PERF_COUNT_HW_CACHE_MISSES]	 = EV67_BCACHEMISS,
};

struct ev67_mapping_t {
	int config;
	int idx;
};

/*
 * The mapping used for one event only - these must be in same order as enum
 * ev67_pmc_event_type definition.
 */
static const struct ev67_mapping_t ev67_mapping[] = {
	{EV67_PCTR_INSTR_CYCLES, 1},	 /* EV67_CYCLES, */
	{EV67_PCTR_INSTR_CYCLES, 0},	 /* EV67_INSTRUCTIONS */
	{EV67_PCTR_INSTR_BCACHEMISS, 1}, /* EV67_BCACHEMISS */
	{EV67_PCTR_CYCLES_MBOX, 1}	 /* EV67_MBOXREPLAY */
};


/*
 * Check that a group of events can be simultaneously scheduled on to the
 * EV67 PMU.  Also allocate counter indices and config.
 */
static int ev67_check_constraints(struct perf_event **event,
				unsigned long *evtype, int n_ev)
{
	int idx0;
	unsigned long config;

	idx0 = ev67_mapping[evtype[0]-1].idx;
	config = ev67_mapping[evtype[0]-1].config;
	if (n_ev == 1)
		goto success;

	BUG_ON(n_ev != 2);

	if (evtype[0] == EV67_MBOXREPLAY || evtype[1] == EV67_MBOXREPLAY) {
		/* MBOX replay traps must be on PMC 1 */
		idx0 = (evtype[0] == EV67_MBOXREPLAY) ? 1 : 0;
		/* Only cycles can accompany MBOX replay traps */
		if (evtype[idx0] == EV67_CYCLES) {
			config = EV67_PCTR_CYCLES_MBOX;
			goto success;
		}
	}

	if (evtype[0] == EV67_BCACHEMISS || evtype[1] == EV67_BCACHEMISS) {
		/* Bcache misses must be on PMC 1 */
		idx0 = (evtype[0] == EV67_BCACHEMISS) ? 1 : 0;
		/* Only instructions can accompany Bcache misses */
		if (evtype[idx0] == EV67_INSTRUCTIONS) {
			config = EV67_PCTR_INSTR_BCACHEMISS;
			goto success;
		}
	}

	if (evtype[0] == EV67_INSTRUCTIONS || evtype[1] == EV67_INSTRUCTIONS) {
		/* Instructions must be on PMC 0 */
		idx0 = (evtype[0] == EV67_INSTRUCTIONS) ? 0 : 1;
		/* By this point only cycles can accompany instructions */
		if (evtype[idx0^1] == EV67_CYCLES) {
			config = EV67_PCTR_INSTR_CYCLES;
			goto success;
		}
	}

	/* Otherwise, darn it, there is a conflict.  */
	return -1;

success:
	event[0]->hw.idx = idx0;
	event[0]->hw.config_base = config;
	if (n_ev == 2) {
		event[1]->hw.idx = idx0 ^ 1;
		event[1]->hw.config_base = config;
	}
	return 0;
}


static const struct alpha_pmu_t ev67_pmu = {
	.event_map = ev67_perfmon_event_map,
	.max_events = ARRAY_SIZE(ev67_perfmon_event_map),
	.num_pmcs = 2,
	.pmc_count_shift = {EV67_PCTR_0_COUNT_SHIFT, EV67_PCTR_1_COUNT_SHIFT, 0},
	.pmc_count_mask = {EV67_PCTR_0_COUNT_MASK,  EV67_PCTR_1_COUNT_MASK,  0},
	.pmc_max_period = {(1UL<<20) - 1, (1UL<<20) - 1, 0},
	.pmc_left = {16, 4, 0},
	.check_constraints = ev67_check_constraints
};



/*
 * Helper routines to ensure that we read/write only the correct PMC bits
 * when calling the wrperfmon PALcall.
 */
static inline void alpha_write_pmc(int idx, unsigned long val)
{
	val &= alpha_pmu->pmc_count_mask[idx];
	val <<= alpha_pmu->pmc_count_shift[idx];
	val |= (1<<idx);
	wrperfmon(PERFMON_CMD_WRITE, val);
}

static inline unsigned long alpha_read_pmc(int idx)
{
	unsigned long val;

	val = wrperfmon(PERFMON_CMD_READ, 0);
	val >>= alpha_pmu->pmc_count_shift[idx];
	val &= alpha_pmu->pmc_count_mask[idx];
	return val;
}

/* Set a new period to sample over */
static int alpha_perf_event_set_period(struct perf_event *event,
				struct hw_perf_event *hwc, int idx)
{
	long left = local64_read(&hwc->period_left);
	long period = hwc->sample_period;
	int ret = 0;

	if (unlikely(left <= -period)) {
		left = period;
		local64_set(&hwc->period_left, left);
		hwc->last_period = period;
		ret = 1;
	}

	if (unlikely(left <= 0)) {
		left += period;
		local64_set(&hwc->period_left, left);
		hwc->last_period = period;
		ret = 1;
	}

	/*
	 * Hardware restrictions require that the counters must not be
	 * written with values that are too close to the maximum period.
	 */
	if (unlikely(left < alpha_pmu->pmc_left[idx]))
		left = alpha_pmu->pmc_left[idx];

	if (left > (long)alpha_pmu->pmc_max_period[idx])
		left = alpha_pmu->pmc_max_period[idx];

	local64_set(&hwc->prev_count, (unsigned long)(-left));

	alpha_write_pmc(idx, (unsigned long)(-left));

	perf_event_update_userpage(event);

	return ret;
}


/*
 * Calculates the count (the 'delta') since the last time the PMC was read.
 *
 * As the PMCs' full period can easily be exceeded within the perf system
 * sampling period we cannot use any high order bits as a guard bit in the
 * PMCs to detect overflow as is done by other architectures.  The code here
 * calculates the delta on the basis that there is no overflow when ovf is
 * zero.  The value passed via ovf by the interrupt handler corrects for
 * overflow.
 *
 * This can be racey on rare occasions -- a call to this routine can occur
 * with an overflowed counter just before the PMI service routine is called.
 * The check for delta negative hopefully always rectifies this situation.
 */
static unsigned long alpha_perf_event_update(struct perf_event *event,
					struct hw_perf_event *hwc, int idx, long ovf)
{
	long prev_raw_count, new_raw_count;
	long delta;

again:
	prev_raw_count = local64_read(&hwc->prev_count);
	new_raw_count = alpha_read_pmc(idx);

	if (local64_cmpxchg(&hwc->prev_count, prev_raw_count,
			     new_raw_count) != prev_raw_count)
		goto again;

	delta = (new_raw_count  - (prev_raw_count & alpha_pmu->pmc_count_mask[idx])) + ovf;

	/* It is possible on very rare occasions that the PMC has overflowed
	 * but the interrupt is yet to come.  Detect and fix this situation.
	 */
	if (unlikely(delta < 0)) {
		delta += alpha_pmu->pmc_max_period[idx] + 1;
	}

	local64_add(delta, &event->count);
	local64_sub(delta, &hwc->period_left);

	return new_raw_count;
}


/*
 * Collect all HW events into the array event[].
 */
static int collect_events(struct perf_event *group, int max_count,
			  struct perf_event *event[], unsigned long *evtype,
			  int *current_idx)
{
	struct perf_event *pe;
	int n = 0;

	if (!is_software_event(group)) {
		if (n >= max_count)
			return -1;
		event[n] = group;
		evtype[n] = group->hw.event_base;
		current_idx[n++] = PMC_NO_INDEX;
	}
	list_for_each_entry(pe, &group->sibling_list, group_entry) {
		if (!is_software_event(pe) && pe->state != PERF_EVENT_STATE_OFF) {
			if (n >= max_count)
				return -1;
			event[n] = pe;
			evtype[n] = pe->hw.event_base;
			current_idx[n++] = PMC_NO_INDEX;
		}
	}
	return n;
}



/*
 * Check that a group of events can be simultaneously scheduled on to the PMU.
 */
static int alpha_check_constraints(struct perf_event **events,
				   unsigned long *evtypes, int n_ev)
{

	/* No HW events is possible from hw_perf_group_sched_in(). */
	if (n_ev == 0)
		return 0;

	if (n_ev > alpha_pmu->num_pmcs)
		return -1;

	return alpha_pmu->check_constraints(events, evtypes, n_ev);
}


/*
 * If new events have been scheduled then update cpuc with the new
 * configuration.  This may involve shifting cycle counts from one PMC to
 * another.
 */
static void maybe_change_configuration(struct cpu_hw_events *cpuc)
{
	int j;

	if (cpuc->n_added == 0)
		return;

	/* Find counters that are moving to another PMC and update */
	for (j = 0; j < cpuc->n_events; j++) {
		struct perf_event *pe = cpuc->event[j];

		if (cpuc->current_idx[j] != PMC_NO_INDEX &&
			cpuc->current_idx[j] != pe->hw.idx) {
			alpha_perf_event_update(pe, &pe->hw, cpuc->current_idx[j], 0);
			cpuc->current_idx[j] = PMC_NO_INDEX;
		}
	}

	/* Assign to counters all unassigned events. */
	cpuc->idx_mask = 0;
	for (j = 0; j < cpuc->n_events; j++) {
		struct perf_event *pe = cpuc->event[j];
		struct hw_perf_event *hwc = &pe->hw;
		int idx = hwc->idx;

		if (cpuc->current_idx[j] != PMC_NO_INDEX) {
			cpuc->idx_mask |= (1<<cpuc->current_idx[j]);
			continue;
		}

		alpha_perf_event_set_period(pe, hwc, idx);
		cpuc->current_idx[j] = idx;
		cpuc->idx_mask |= (1<<cpuc->current_idx[j]);
	}
	cpuc->config = cpuc->event[0]->hw.config_base;
}



/* Schedule perf HW event on to PMU.
 *  - this function is called from outside this module via the pmu struct
 *    returned from perf event initialisation.
 */
static int alpha_pmu_enable(struct perf_event *event)
{
	struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
	int n0;
	int ret;
	unsigned long flags;

	/*
	 * The Sparc code has the IRQ disable first followed by the perf
	 * disable, however this can lead to an overflowed counter with the
	 * PMI disabled on rare occasions.  The alpha_perf_event_update()
	 * routine should detect this situation by noting a negative delta,
	 * nevertheless we disable the PMCs first to enable a potential
	 * final PMI to occur before we disable interrupts.
	 */
	perf_disable();
	local_irq_save(flags);

	/* Default to error to be returned */
	ret = -EAGAIN;

	/* Insert event on to PMU and if successful modify ret to valid return */
	n0 = cpuc->n_events;
	if (n0 < alpha_pmu->num_pmcs) {
		cpuc->event[n0] = event;
		cpuc->evtype[n0] = event->hw.event_base;
		cpuc->current_idx[n0] = PMC_NO_INDEX;

		if (!alpha_check_constraints(cpuc->event, cpuc->evtype, n0+1)) {
			cpuc->n_events++;
			cpuc->n_added++;
			ret = 0;
		}
	}

	local_irq_restore(flags);
	perf_enable();

	return ret;
}



/* Disable performance monitoring unit
 *  - this function is called from outside this module via the pmu struct
 *    returned from perf event initialisation.
 */
static void alpha_pmu_disable(struct perf_event *event)
{
	struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
	struct hw_perf_event *hwc = &event->hw;
	unsigned long flags;
	int j;

	perf_disable();
	local_irq_save(flags);

	for (j = 0; j < cpuc->n_events; j++) {
		if (event == cpuc->event[j]) {
			int idx = cpuc->current_idx[j];

			/* Shift remaining entries down into the existing
			 * slot.
			 */
			while (++j < cpuc->n_events) {
				cpuc->event[j - 1] = cpuc->event[j];
				cpuc->evtype[j - 1] = cpuc->evtype[j];
				cpuc->current_idx[j - 1] =
					cpuc->current_idx[j];
			}

			/* Absorb the final count and turn off the event. */
			alpha_perf_event_update(event, hwc, idx, 0);
			perf_event_update_userpage(event);

			cpuc->idx_mask &= ~(1UL<<idx);
			cpuc->n_events--;
			break;
		}
	}

	local_irq_restore(flags);
	perf_enable();
}


static void alpha_pmu_read(struct perf_event *event)
{
	struct hw_perf_event *hwc = &event->hw;

	alpha_perf_event_update(event, hwc, hwc->idx, 0);
}


static void alpha_pmu_unthrottle(struct perf_event *event)
{
	struct hw_perf_event *hwc = &event->hw;
	struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);

	cpuc->idx_mask |= 1UL<<hwc->idx;
	wrperfmon(PERFMON_CMD_ENABLE, (1UL<<hwc->idx));
}


/*
 * Check that CPU performance counters are supported.
 * - currently support EV67 and later CPUs.
 * - actually some later revisions of the EV6 have the same PMC model as the
 *     EV67 but we don't do suffiently deep CPU detection to detect them.
 *     Bad luck to the very few people who might have one, I guess.
 */
static int supported_cpu(void)
{
	struct percpu_struct *cpu;
	unsigned long cputype;

	/* Get cpu type from HW */
	cpu = (struct percpu_struct *)((char *)hwrpb + hwrpb->processor_offset);
	cputype = cpu->type & 0xffffffff;
	/* Include all of EV67, EV68, EV7, EV79 and EV69 as supported. */
	return (cputype >= EV67_CPU) && (cputype <= EV69_CPU);
}



static void hw_perf_event_destroy(struct perf_event *event)
{
	/* Nothing to be done! */
	return;
}



static int __hw_perf_event_init(struct perf_event *event)
{
	struct perf_event_attr *attr = &event->attr;
	struct hw_perf_event *hwc = &event->hw;
	struct perf_event *evts[MAX_HWEVENTS];
	unsigned long evtypes[MAX_HWEVENTS];
	int idx_rubbish_bin[MAX_HWEVENTS];
	int ev;
	int n;

	/* We only support a limited range of HARDWARE event types with one
	 * only programmable via a RAW event type.
	 */
	if (attr->type == PERF_TYPE_HARDWARE) {
		if (attr->config >= alpha_pmu->max_events)
			return -EINVAL;
		ev = alpha_pmu->event_map[attr->config];
	} else if (attr->type == PERF_TYPE_HW_CACHE) {
		return -EOPNOTSUPP;
	} else if (attr->type == PERF_TYPE_RAW) {
		ev = attr->config & 0xff;
	} else {
		return -EOPNOTSUPP;
	}

	if (ev < 0) {
		return ev;
	}

	/* The EV67 does not support mode exclusion */
	if (attr->exclude_kernel || attr->exclude_user
			|| attr->exclude_hv || attr->exclude_idle) {
		return -EPERM;
	}

	/*
	 * We place the event type in event_base here and leave calculation
	 * of the codes to programme the PMU for alpha_pmu_enable() because
	 * it is only then we will know what HW events are actually
	 * scheduled on to the PMU.  At that point the code to programme the
	 * PMU is put into config_base and the PMC to use is placed into
	 * idx.  We initialise idx (below) to PMC_NO_INDEX to indicate that
	 * it is yet to be determined.
	 */
	hwc->event_base = ev;

	/* Collect events in a group together suitable for calling
	 * alpha_check_constraints() to verify that the group as a whole can
	 * be scheduled on to the PMU.
	 */
	n = 0;
	if (event->group_leader != event) {
		n = collect_events(event->group_leader,
				alpha_pmu->num_pmcs - 1,
				evts, evtypes, idx_rubbish_bin);
		if (n < 0)
			return -EINVAL;
	}
	evtypes[n] = hwc->event_base;
	evts[n] = event;

	if (alpha_check_constraints(evts, evtypes, n + 1))
		return -EINVAL;

	/* Indicate that PMU config and idx are yet to be determined. */
	hwc->config_base = 0;
	hwc->idx = PMC_NO_INDEX;

	event->destroy = hw_perf_event_destroy;

	/*
	 * Most architectures reserve the PMU for their use at this point.
	 * As there is no existing mechanism to arbitrate usage and there
	 * appears to be no other user of the Alpha PMU we just assume
	 * that we can just use it, hence a NO-OP here.
	 *
	 * Maybe an alpha_reserve_pmu() routine should be implemented but is
	 * anything else ever going to use it?
	 */

	if (!hwc->sample_period) {
		hwc->sample_period = alpha_pmu->pmc_max_period[0];
		hwc->last_period = hwc->sample_period;
		local64_set(&hwc->period_left, hwc->sample_period);
	}

	return 0;
}

static const struct pmu pmu = {
	.enable		= alpha_pmu_enable,
	.disable	= alpha_pmu_disable,
	.read		= alpha_pmu_read,
	.unthrottle	= alpha_pmu_unthrottle,
};


/*
 * Main entry point to initialise a HW performance event.
 */
const struct pmu *hw_perf_event_init(struct perf_event *event)
{
	int err;

	if (!alpha_pmu)
		return ERR_PTR(-ENODEV);

	/* Do the real initialisation work. */
	err = __hw_perf_event_init(event);

	if (err)
		return ERR_PTR(err);

	return &pmu;
}



/*
 * Main entry point - enable HW performance counters.
 */
void hw_perf_enable(void)
{
	struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);

	if (cpuc->enabled)
		return;

	cpuc->enabled = 1;
	barrier();

	if (cpuc->n_events > 0) {
		/* Update cpuc with information from any new scheduled events. */
		maybe_change_configuration(cpuc);

		/* Start counting the desired events. */
		wrperfmon(PERFMON_CMD_LOGGING_OPTIONS, EV67_PCTR_MODE_AGGREGATE);
		wrperfmon(PERFMON_CMD_DESIRED_EVENTS, cpuc->config);
		wrperfmon(PERFMON_CMD_ENABLE, cpuc->idx_mask);
	}
}


/*
 * Main entry point - disable HW performance counters.
 */

void hw_perf_disable(void)
{
	struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);

	if (!cpuc->enabled)
		return;

	cpuc->enabled = 0;
	cpuc->n_added = 0;

	wrperfmon(PERFMON_CMD_DISABLE, cpuc->idx_mask);
}


/*
 * Main entry point - don't know when this is called but it
 * obviously dumps debug info.
 */
void perf_event_print_debug(void)
{
	unsigned long flags;
	unsigned long pcr;
	int pcr0, pcr1;
	int cpu;

	if (!supported_cpu())
		return;

	local_irq_save(flags);

	cpu = smp_processor_id();

	pcr = wrperfmon(PERFMON_CMD_READ, 0);
	pcr0 = (pcr >> alpha_pmu->pmc_count_shift[0]) & alpha_pmu->pmc_count_mask[0];
	pcr1 = (pcr >> alpha_pmu->pmc_count_shift[1]) & alpha_pmu->pmc_count_mask[1];

	pr_info("CPU#%d: PCTR0[%06x] PCTR1[%06x]\n", cpu, pcr0, pcr1);

	local_irq_restore(flags);
}


/*
 * Performance Monitoring Interrupt Service Routine called when a PMC
 * overflows.  The PMC that overflowed is passed in la_ptr.
 */
static void alpha_perf_event_irq_handler(unsigned long la_ptr,
					struct pt_regs *regs)
{
	struct cpu_hw_events *cpuc;
	struct perf_sample_data data;
	struct perf_event *event;
	struct hw_perf_event *hwc;
	int idx, j;

	__get_cpu_var(irq_pmi_count)++;
	cpuc = &__get_cpu_var(cpu_hw_events);

	/* Completely counting through the PMC's period to trigger a new PMC
	 * overflow interrupt while in this interrupt routine is utterly
	 * disastrous!  The EV6 and EV67 counters are sufficiently large to
	 * prevent this but to be really sure disable the PMCs.
	 */
	wrperfmon(PERFMON_CMD_DISABLE, cpuc->idx_mask);

	/* la_ptr is the counter that overflowed. */
	if (unlikely(la_ptr >= perf_max_events)) {
		/* This should never occur! */
		irq_err_count++;
		pr_warning("PMI: silly index %ld\n", la_ptr);
		wrperfmon(PERFMON_CMD_ENABLE, cpuc->idx_mask);
		return;
	}

	idx = la_ptr;

	perf_sample_data_init(&data, 0);
	for (j = 0; j < cpuc->n_events; j++) {
		if (cpuc->current_idx[j] == idx)
			break;
	}

	if (unlikely(j == cpuc->n_events)) {
		/* This can occur if the event is disabled right on a PMC overflow. */
		wrperfmon(PERFMON_CMD_ENABLE, cpuc->idx_mask);
		return;
	}

	event = cpuc->event[j];

	if (unlikely(!event)) {
		/* This should never occur! */
		irq_err_count++;
		pr_warning("PMI: No event at index %d!\n", idx);
		wrperfmon(PERFMON_CMD_ENABLE, cpuc->idx_mask);
		return;
	}

	hwc = &event->hw;
	alpha_perf_event_update(event, hwc, idx, alpha_pmu->pmc_max_period[idx]+1);
	data.period = event->hw.last_period;

	if (alpha_perf_event_set_period(event, hwc, idx)) {
		if (perf_event_overflow(event, 1, &data, regs)) {
			/* Interrupts coming too quickly; "throttle" the
			 * counter, i.e., disable it for a little while.
			 */
			cpuc->idx_mask &= ~(1UL<<idx);
		}
	}
	wrperfmon(PERFMON_CMD_ENABLE, cpuc->idx_mask);

	return;
}



/*
 * Init call to initialise performance events at kernel startup.
 */
void __init init_hw_perf_events(void)
{
	pr_info("Performance events: ");

	if (!supported_cpu()) {
		pr_cont("No support for your CPU.\n");
		return;
	}

	pr_cont("Supported CPU type!\n");

	/* Override performance counter IRQ vector */

	perf_irq = alpha_perf_event_irq_handler;

	/* And set up PMU specification */
	alpha_pmu = &ev67_pmu;
	perf_max_events = alpha_pmu->num_pmcs;
}