perf_counter.c 21.4 KB
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/*
 * Performance counter core code
 *
 *  Copyright(C) 2008 Thomas Gleixner <tglx@linutronix.de>
 *  Copyright(C) 2008 Red Hat, Inc., Ingo Molnar
 *
 *  For licencing details see kernel-base/COPYING
 */

#include <linux/fs.h>
#include <linux/cpu.h>
#include <linux/smp.h>
#include <linux/poll.h>
#include <linux/sysfs.h>
#include <linux/ptrace.h>
#include <linux/percpu.h>
#include <linux/uaccess.h>
#include <linux/syscalls.h>
#include <linux/anon_inodes.h>
#include <linux/perf_counter.h>

/*
 * Each CPU has a list of per CPU counters:
 */
DEFINE_PER_CPU(struct perf_cpu_context, perf_cpu_context);

int perf_max_counters __read_mostly;
static int perf_reserved_percpu __read_mostly;
static int perf_overcommit __read_mostly = 1;

/*
 * Mutex for (sysadmin-configurable) counter reservations:
 */
static DEFINE_MUTEX(perf_resource_mutex);

/*
 * Architecture provided APIs - weak aliases:
 */

int __weak hw_perf_counter_init(struct perf_counter *counter, u32 hw_event_type)
{
	return -EINVAL;
}

void __weak hw_perf_counter_enable(struct perf_counter *counter)	 { }
void __weak hw_perf_counter_disable(struct perf_counter *counter)	 { }
void __weak hw_perf_counter_read(struct perf_counter *counter)		 { }
void __weak hw_perf_disable_all(void) { }
void __weak hw_perf_enable_all(void) { }
void __weak hw_perf_counter_setup(void) { }

#if BITS_PER_LONG == 64

/*
 * Read the cached counter in counter safe against cross CPU / NMI
 * modifications. 64 bit version - no complications.
 */
static inline u64 perf_read_counter_safe(struct perf_counter *counter)
{
	return (u64) atomic64_read(&counter->count);
}

#else

/*
 * Read the cached counter in counter safe against cross CPU / NMI
 * modifications. 32 bit version.
 */
static u64 perf_read_counter_safe(struct perf_counter *counter)
{
	u32 cntl, cnth;

	local_irq_disable();
	do {
		cnth = atomic_read(&counter->count32[1]);
		cntl = atomic_read(&counter->count32[0]);
	} while (cnth != atomic_read(&counter->count32[1]));

	local_irq_enable();

	return cntl | ((u64) cnth) << 32;
}

#endif

/*
 * Cross CPU call to remove a performance counter
 *
 * We disable the counter on the hardware level first. After that we
 * remove it from the context list.
 */
static void __perf_remove_from_context(void *info)
{
	struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
	struct perf_counter *counter = info;
	struct perf_counter_context *ctx = counter->ctx;

	/*
	 * If this is a task context, we need to check whether it is
	 * the current task context of this cpu. If not it has been
	 * scheduled out before the smp call arrived.
	 */
	if (ctx->task && cpuctx->task_ctx != ctx)
		return;

	spin_lock(&ctx->lock);

	if (counter->active) {
		hw_perf_counter_disable(counter);
		counter->active = 0;
		ctx->nr_active--;
		cpuctx->active_oncpu--;
		counter->task = NULL;
	}
	ctx->nr_counters--;

	/*
	 * Protect the list operation against NMI by disabling the
	 * counters on a global level. NOP for non NMI based counters.
	 */
	hw_perf_disable_all();
	list_del_init(&counter->list);
	hw_perf_enable_all();

	if (!ctx->task) {
		/*
		 * Allow more per task counters with respect to the
		 * reservation:
		 */
		cpuctx->max_pertask =
			min(perf_max_counters - ctx->nr_counters,
			    perf_max_counters - perf_reserved_percpu);
	}

	spin_unlock(&ctx->lock);
}


/*
 * Remove the counter from a task's (or a CPU's) list of counters.
 *
 * Must be called with counter->mutex held.
 *
 * CPU counters are removed with a smp call. For task counters we only
 * call when the task is on a CPU.
 */
static void perf_remove_from_context(struct perf_counter *counter)
{
	struct perf_counter_context *ctx = counter->ctx;
	struct task_struct *task = ctx->task;

	if (!task) {
		/*
		 * Per cpu counters are removed via an smp call and
		 * the removal is always sucessful.
		 */
		smp_call_function_single(counter->cpu,
					 __perf_remove_from_context,
					 counter, 1);
		return;
	}

retry:
	task_oncpu_function_call(task, __perf_remove_from_context,
				 counter);

	spin_lock_irq(&ctx->lock);
	/*
	 * If the context is active we need to retry the smp call.
	 */
	if (ctx->nr_active && !list_empty(&counter->list)) {
		spin_unlock_irq(&ctx->lock);
		goto retry;
	}

	/*
	 * The lock prevents that this context is scheduled in so we
	 * can remove the counter safely, if it the call above did not
	 * succeed.
	 */
	if (!list_empty(&counter->list)) {
		ctx->nr_counters--;
		list_del_init(&counter->list);
		counter->task = NULL;
	}
	spin_unlock_irq(&ctx->lock);
}

/*
 * Cross CPU call to install and enable a preformance counter
 */
static void __perf_install_in_context(void *info)
{
	struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
	struct perf_counter *counter = info;
	struct perf_counter_context *ctx = counter->ctx;
	int cpu = smp_processor_id();

	/*
	 * If this is a task context, we need to check whether it is
	 * the current task context of this cpu. If not it has been
	 * scheduled out before the smp call arrived.
	 */
	if (ctx->task && cpuctx->task_ctx != ctx)
		return;

	spin_lock(&ctx->lock);

	/*
	 * Protect the list operation against NMI by disabling the
	 * counters on a global level. NOP for non NMI based counters.
	 */
	hw_perf_disable_all();
	list_add_tail(&counter->list, &ctx->counters);
	hw_perf_enable_all();

	ctx->nr_counters++;

	if (cpuctx->active_oncpu < perf_max_counters) {
		hw_perf_counter_enable(counter);
		counter->active = 1;
		counter->oncpu = cpu;
		ctx->nr_active++;
		cpuctx->active_oncpu++;
	}

	if (!ctx->task && cpuctx->max_pertask)
		cpuctx->max_pertask--;

	spin_unlock(&ctx->lock);
}

/*
 * Attach a performance counter to a context
 *
 * First we add the counter to the list with the hardware enable bit
 * in counter->hw_config cleared.
 *
 * If the counter is attached to a task which is on a CPU we use a smp
 * call to enable it in the task context. The task might have been
 * scheduled away, but we check this in the smp call again.
 */
static void
perf_install_in_context(struct perf_counter_context *ctx,
			struct perf_counter *counter,
			int cpu)
{
	struct task_struct *task = ctx->task;

	counter->ctx = ctx;
	if (!task) {
		/*
		 * Per cpu counters are installed via an smp call and
		 * the install is always sucessful.
		 */
		smp_call_function_single(cpu, __perf_install_in_context,
					 counter, 1);
		return;
	}

	counter->task = task;
retry:
	task_oncpu_function_call(task, __perf_install_in_context,
				 counter);

	spin_lock_irq(&ctx->lock);
	/*
	 * If the context is active and the counter has not been added
	 * we need to retry the smp call.
	 */
	if (ctx->nr_active && list_empty(&counter->list)) {
		spin_unlock_irq(&ctx->lock);
		goto retry;
	}

	/*
	 * The lock prevents that this context is scheduled in so we
	 * can add the counter safely, if it the call above did not
	 * succeed.
	 */
	if (list_empty(&counter->list)) {
		list_add_tail(&counter->list, &ctx->counters);
		ctx->nr_counters++;
	}
	spin_unlock_irq(&ctx->lock);
}

/*
 * Called from scheduler to remove the counters of the current task,
 * with interrupts disabled.
 *
 * We stop each counter and update the counter value in counter->count.
 *
 * This does not protect us against NMI, but hw_perf_counter_disable()
 * sets the disabled bit in the control field of counter _before_
 * accessing the counter control register. If a NMI hits, then it will
 * not restart the counter.
 */
void perf_counter_task_sched_out(struct task_struct *task, int cpu)
{
	struct perf_cpu_context *cpuctx = &per_cpu(perf_cpu_context, cpu);
	struct perf_counter_context *ctx = &task->perf_counter_ctx;
	struct perf_counter *counter;

	if (likely(!cpuctx->task_ctx))
		return;

	spin_lock(&ctx->lock);
	list_for_each_entry(counter, &ctx->counters, list) {
		if (!ctx->nr_active)
			break;
		if (counter->active) {
			hw_perf_counter_disable(counter);
			counter->active = 0;
			counter->oncpu = -1;
			ctx->nr_active--;
			cpuctx->active_oncpu--;
		}
	}
	spin_unlock(&ctx->lock);
	cpuctx->task_ctx = NULL;
}

/*
 * Called from scheduler to add the counters of the current task
 * with interrupts disabled.
 *
 * We restore the counter value and then enable it.
 *
 * This does not protect us against NMI, but hw_perf_counter_enable()
 * sets the enabled bit in the control field of counter _before_
 * accessing the counter control register. If a NMI hits, then it will
 * keep the counter running.
 */
void perf_counter_task_sched_in(struct task_struct *task, int cpu)
{
	struct perf_cpu_context *cpuctx = &per_cpu(perf_cpu_context, cpu);
	struct perf_counter_context *ctx = &task->perf_counter_ctx;
	struct perf_counter *counter;

	if (likely(!ctx->nr_counters))
		return;

	spin_lock(&ctx->lock);
	list_for_each_entry(counter, &ctx->counters, list) {
		if (ctx->nr_active == cpuctx->max_pertask)
			break;
		if (counter->cpu != -1 && counter->cpu != cpu)
			continue;

		hw_perf_counter_enable(counter);
		counter->active = 1;
		counter->oncpu = cpu;
		ctx->nr_active++;
		cpuctx->active_oncpu++;
	}
	spin_unlock(&ctx->lock);
	cpuctx->task_ctx = ctx;
}

void perf_counter_task_tick(struct task_struct *curr, int cpu)
{
	struct perf_counter_context *ctx = &curr->perf_counter_ctx;
	struct perf_counter *counter;

	if (likely(!ctx->nr_counters))
		return;

	perf_counter_task_sched_out(curr, cpu);

	spin_lock(&ctx->lock);

	/*
	 * Rotate the first entry last:
	 */
	hw_perf_disable_all();
	list_for_each_entry(counter, &ctx->counters, list) {
		list_del(&counter->list);
		list_add_tail(&counter->list, &ctx->counters);
		break;
	}
	hw_perf_enable_all();

	spin_unlock(&ctx->lock);

	perf_counter_task_sched_in(curr, cpu);
}

/*
 * Initialize the perf_counter context in task_struct
 */
void perf_counter_init_task(struct task_struct *task)
{
	struct perf_counter_context *ctx = &task->perf_counter_ctx;

	spin_lock_init(&ctx->lock);
	INIT_LIST_HEAD(&ctx->counters);
	ctx->nr_counters = 0;
	ctx->task = task;
}

/*
 * Cross CPU call to read the hardware counter
 */
static void __hw_perf_counter_read(void *info)
{
	hw_perf_counter_read(info);
}

static u64 perf_read_counter(struct perf_counter *counter)
{
	/*
	 * If counter is enabled and currently active on a CPU, update the
	 * value in the counter structure:
	 */
	if (counter->active) {
		smp_call_function_single(counter->oncpu,
					 __hw_perf_counter_read, counter, 1);
	}

	return perf_read_counter_safe(counter);
}

/*
 * Cross CPU call to switch performance data pointers
 */
static void __perf_switch_irq_data(void *info)
{
	struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
	struct perf_counter *counter = info;
	struct perf_counter_context *ctx = counter->ctx;
	struct perf_data *oldirqdata = counter->irqdata;

	/*
	 * If this is a task context, we need to check whether it is
	 * the current task context of this cpu. If not it has been
	 * scheduled out before the smp call arrived.
	 */
	if (ctx->task) {
		if (cpuctx->task_ctx != ctx)
			return;
		spin_lock(&ctx->lock);
	}

	/* Change the pointer NMI safe */
	atomic_long_set((atomic_long_t *)&counter->irqdata,
			(unsigned long) counter->usrdata);
	counter->usrdata = oldirqdata;

	if (ctx->task)
		spin_unlock(&ctx->lock);
}

static struct perf_data *perf_switch_irq_data(struct perf_counter *counter)
{
	struct perf_counter_context *ctx = counter->ctx;
	struct perf_data *oldirqdata = counter->irqdata;
	struct task_struct *task = ctx->task;

	if (!task) {
		smp_call_function_single(counter->cpu,
					 __perf_switch_irq_data,
					 counter, 1);
		return counter->usrdata;
	}

retry:
	spin_lock_irq(&ctx->lock);
	if (!counter->active) {
		counter->irqdata = counter->usrdata;
		counter->usrdata = oldirqdata;
		spin_unlock_irq(&ctx->lock);
		return oldirqdata;
	}
	spin_unlock_irq(&ctx->lock);
	task_oncpu_function_call(task, __perf_switch_irq_data, counter);
	/* Might have failed, because task was scheduled out */
	if (counter->irqdata == oldirqdata)
		goto retry;

	return counter->usrdata;
}

static void put_context(struct perf_counter_context *ctx)
{
	if (ctx->task)
		put_task_struct(ctx->task);
}

static struct perf_counter_context *find_get_context(pid_t pid, int cpu)
{
	struct perf_cpu_context *cpuctx;
	struct perf_counter_context *ctx;
	struct task_struct *task;

	/*
	 * If cpu is not a wildcard then this is a percpu counter:
	 */
	if (cpu != -1) {
		/* Must be root to operate on a CPU counter: */
		if (!capable(CAP_SYS_ADMIN))
			return ERR_PTR(-EACCES);

		if (cpu < 0 || cpu > num_possible_cpus())
			return ERR_PTR(-EINVAL);

		/*
		 * We could be clever and allow to attach a counter to an
		 * offline CPU and activate it when the CPU comes up, but
		 * that's for later.
		 */
		if (!cpu_isset(cpu, cpu_online_map))
			return ERR_PTR(-ENODEV);

		cpuctx = &per_cpu(perf_cpu_context, cpu);
		ctx = &cpuctx->ctx;

		WARN_ON_ONCE(ctx->task);
		return ctx;
	}

	rcu_read_lock();
	if (!pid)
		task = current;
	else
		task = find_task_by_vpid(pid);
	if (task)
		get_task_struct(task);
	rcu_read_unlock();

	if (!task)
		return ERR_PTR(-ESRCH);

	ctx = &task->perf_counter_ctx;
	ctx->task = task;

	/* Reuse ptrace permission checks for now. */
	if (!ptrace_may_access(task, PTRACE_MODE_READ)) {
		put_context(ctx);
		return ERR_PTR(-EACCES);
	}

	return ctx;
}

/*
 * Called when the last reference to the file is gone.
 */
static int perf_release(struct inode *inode, struct file *file)
{
	struct perf_counter *counter = file->private_data;
	struct perf_counter_context *ctx = counter->ctx;

	file->private_data = NULL;

	mutex_lock(&counter->mutex);

	perf_remove_from_context(counter);
	put_context(ctx);

	mutex_unlock(&counter->mutex);

	kfree(counter);

	return 0;
}

/*
 * Read the performance counter - simple non blocking version for now
 */
static ssize_t
perf_read_hw(struct perf_counter *counter, char __user *buf, size_t count)
{
	u64 cntval;

	if (count != sizeof(cntval))
		return -EINVAL;

	mutex_lock(&counter->mutex);
	cntval = perf_read_counter(counter);
	mutex_unlock(&counter->mutex);

	return put_user(cntval, (u64 __user *) buf) ? -EFAULT : sizeof(cntval);
}

static ssize_t
perf_copy_usrdata(struct perf_data *usrdata, char __user *buf, size_t count)
{
	if (!usrdata->len)
		return 0;

	count = min(count, (size_t)usrdata->len);
	if (copy_to_user(buf, usrdata->data + usrdata->rd_idx, count))
		return -EFAULT;

	/* Adjust the counters */
	usrdata->len -= count;
	if (!usrdata->len)
		usrdata->rd_idx = 0;
	else
		usrdata->rd_idx += count;

	return count;
}

static ssize_t
perf_read_irq_data(struct perf_counter	*counter,
		   char __user		*buf,
		   size_t		count,
		   int			nonblocking)
{
	struct perf_data *irqdata, *usrdata;
	DECLARE_WAITQUEUE(wait, current);
	ssize_t res;

	irqdata = counter->irqdata;
	usrdata = counter->usrdata;

	if (usrdata->len + irqdata->len >= count)
		goto read_pending;

	if (nonblocking)
		return -EAGAIN;

	spin_lock_irq(&counter->waitq.lock);
	__add_wait_queue(&counter->waitq, &wait);
	for (;;) {
		set_current_state(TASK_INTERRUPTIBLE);
		if (usrdata->len + irqdata->len >= count)
			break;

		if (signal_pending(current))
			break;

		spin_unlock_irq(&counter->waitq.lock);
		schedule();
		spin_lock_irq(&counter->waitq.lock);
	}
	__remove_wait_queue(&counter->waitq, &wait);
	__set_current_state(TASK_RUNNING);
	spin_unlock_irq(&counter->waitq.lock);

	if (usrdata->len + irqdata->len < count)
		return -ERESTARTSYS;
read_pending:
	mutex_lock(&counter->mutex);

	/* Drain pending data first: */
	res = perf_copy_usrdata(usrdata, buf, count);
	if (res < 0 || res == count)
		goto out;

	/* Switch irq buffer: */
	usrdata = perf_switch_irq_data(counter);
	if (perf_copy_usrdata(usrdata, buf + res, count - res) < 0) {
		if (!res)
			res = -EFAULT;
	} else {
		res = count;
	}
out:
	mutex_unlock(&counter->mutex);

	return res;
}

static ssize_t
perf_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
{
	struct perf_counter *counter = file->private_data;

	switch (counter->record_type) {
	case PERF_RECORD_SIMPLE:
		return perf_read_hw(counter, buf, count);

	case PERF_RECORD_IRQ:
	case PERF_RECORD_GROUP:
		return perf_read_irq_data(counter, buf, count,
					  file->f_flags & O_NONBLOCK);
	}
	return -EINVAL;
}

static unsigned int perf_poll(struct file *file, poll_table *wait)
{
	struct perf_counter *counter = file->private_data;
	unsigned int events = 0;
	unsigned long flags;

	poll_wait(file, &counter->waitq, wait);

	spin_lock_irqsave(&counter->waitq.lock, flags);
	if (counter->usrdata->len || counter->irqdata->len)
		events |= POLLIN;
	spin_unlock_irqrestore(&counter->waitq.lock, flags);

	return events;
}

static const struct file_operations perf_fops = {
	.release		= perf_release,
	.read			= perf_read,
	.poll			= perf_poll,
};

/*
 * Allocate and initialize a counter structure
 */
static struct perf_counter *
perf_counter_alloc(u32 hw_event_period, int cpu, u32 record_type)
{
	struct perf_counter *counter = kzalloc(sizeof(*counter), GFP_KERNEL);

	if (!counter)
		return NULL;

	mutex_init(&counter->mutex);
	INIT_LIST_HEAD(&counter->list);
	init_waitqueue_head(&counter->waitq);

	counter->irqdata	= &counter->data[0];
	counter->usrdata	= &counter->data[1];
	counter->cpu		= cpu;
	counter->record_type	= record_type;
	counter->__irq_period	= hw_event_period;
	counter->wakeup_pending = 0;

	return counter;
}

/**
 * sys_perf_task_open - open a performance counter associate it to a task
 * @hw_event_type:	event type for monitoring/sampling...
 * @pid:		target pid
 */
asmlinkage int
737 738
sys_perf_counter_open(struct perf_counter_event __user *uevent, u32 record_type,
		      pid_t pid, int cpu, int masterfd)
739 740
{
	struct perf_counter_context *ctx;
741
	struct perf_counter_event event;
742 743 744
	struct perf_counter *counter;
	int ret;

745 746 747
	if (copy_from_user(&event, uevent, sizeof(event)) != 0)
		return -EFAULT;

748 749 750 751 752
	ctx = find_get_context(pid, cpu);
	if (IS_ERR(ctx))
		return PTR_ERR(ctx);

	ret = -ENOMEM;
753
	counter = perf_counter_alloc(event.hw_event_period, cpu, record_type);
754 755 756
	if (!counter)
		goto err_put_context;

757
	ret = hw_perf_counter_init(counter, event.hw_event_type);
758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944
	if (ret)
		goto err_free_put_context;

	perf_install_in_context(ctx, counter, cpu);

	ret = anon_inode_getfd("[perf_counter]", &perf_fops, counter, 0);
	if (ret < 0)
		goto err_remove_free_put_context;

	return ret;

err_remove_free_put_context:
	mutex_lock(&counter->mutex);
	perf_remove_from_context(counter);
	mutex_unlock(&counter->mutex);

err_free_put_context:
	kfree(counter);

err_put_context:
	put_context(ctx);

	return ret;
}

static void __cpuinit perf_init_cpu(int cpu)
{
	struct perf_cpu_context *ctx;

	ctx = &per_cpu(perf_cpu_context, cpu);
	spin_lock_init(&ctx->ctx.lock);
	INIT_LIST_HEAD(&ctx->ctx.counters);

	mutex_lock(&perf_resource_mutex);
	ctx->max_pertask = perf_max_counters - perf_reserved_percpu;
	mutex_unlock(&perf_resource_mutex);
	hw_perf_counter_setup();
}

#ifdef CONFIG_HOTPLUG_CPU
static void __perf_exit_cpu(void *info)
{
	struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
	struct perf_counter_context *ctx = &cpuctx->ctx;
	struct perf_counter *counter, *tmp;

	list_for_each_entry_safe(counter, tmp, &ctx->counters, list)
		__perf_remove_from_context(counter);

}
static void perf_exit_cpu(int cpu)
{
	smp_call_function_single(cpu, __perf_exit_cpu, NULL, 1);
}
#else
static inline void perf_exit_cpu(int cpu) { }
#endif

static int __cpuinit
perf_cpu_notify(struct notifier_block *self, unsigned long action, void *hcpu)
{
	unsigned int cpu = (long)hcpu;

	switch (action) {

	case CPU_UP_PREPARE:
	case CPU_UP_PREPARE_FROZEN:
		perf_init_cpu(cpu);
		break;

	case CPU_DOWN_PREPARE:
	case CPU_DOWN_PREPARE_FROZEN:
		perf_exit_cpu(cpu);
		break;

	default:
		break;
	}

	return NOTIFY_OK;
}

static struct notifier_block __cpuinitdata perf_cpu_nb = {
	.notifier_call		= perf_cpu_notify,
};

static int __init perf_counter_init(void)
{
	perf_cpu_notify(&perf_cpu_nb, (unsigned long)CPU_UP_PREPARE,
			(void *)(long)smp_processor_id());
	register_cpu_notifier(&perf_cpu_nb);

	return 0;
}
early_initcall(perf_counter_init);

static ssize_t perf_show_reserve_percpu(struct sysdev_class *class, char *buf)
{
	return sprintf(buf, "%d\n", perf_reserved_percpu);
}

static ssize_t
perf_set_reserve_percpu(struct sysdev_class *class,
			const char *buf,
			size_t count)
{
	struct perf_cpu_context *cpuctx;
	unsigned long val;
	int err, cpu, mpt;

	err = strict_strtoul(buf, 10, &val);
	if (err)
		return err;
	if (val > perf_max_counters)
		return -EINVAL;

	mutex_lock(&perf_resource_mutex);
	perf_reserved_percpu = val;
	for_each_online_cpu(cpu) {
		cpuctx = &per_cpu(perf_cpu_context, cpu);
		spin_lock_irq(&cpuctx->ctx.lock);
		mpt = min(perf_max_counters - cpuctx->ctx.nr_counters,
			  perf_max_counters - perf_reserved_percpu);
		cpuctx->max_pertask = mpt;
		spin_unlock_irq(&cpuctx->ctx.lock);
	}
	mutex_unlock(&perf_resource_mutex);

	return count;
}

static ssize_t perf_show_overcommit(struct sysdev_class *class, char *buf)
{
	return sprintf(buf, "%d\n", perf_overcommit);
}

static ssize_t
perf_set_overcommit(struct sysdev_class *class, const char *buf, size_t count)
{
	unsigned long val;
	int err;

	err = strict_strtoul(buf, 10, &val);
	if (err)
		return err;
	if (val > 1)
		return -EINVAL;

	mutex_lock(&perf_resource_mutex);
	perf_overcommit = val;
	mutex_unlock(&perf_resource_mutex);

	return count;
}

static SYSDEV_CLASS_ATTR(
				reserve_percpu,
				0644,
				perf_show_reserve_percpu,
				perf_set_reserve_percpu
			);

static SYSDEV_CLASS_ATTR(
				overcommit,
				0644,
				perf_show_overcommit,
				perf_set_overcommit
			);

static struct attribute *perfclass_attrs[] = {
	&attr_reserve_percpu.attr,
	&attr_overcommit.attr,
	NULL
};

static struct attribute_group perfclass_attr_group = {
	.attrs			= perfclass_attrs,
	.name			= "perf_counters",
};

static int __init perf_counter_sysfs_init(void)
{
	return sysfs_create_group(&cpu_sysdev_class.kset.kobj,
				  &perfclass_attr_group);
}
device_initcall(perf_counter_sysfs_init);