linux/kernel/perf_counter.c

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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)
{
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(struct perf_counter_event *event, 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->event = *event;
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
sys_perf_counter_open(struct perf_counter_event __user *uevent, u32 record_type,
pid_t pid, int cpu, int masterfd)
{
struct perf_counter_context *ctx;
struct perf_counter_event event;
struct perf_counter *counter;
int ret;
if (copy_from_user(&event, uevent, sizeof(event)) != 0)
return -EFAULT;
ctx = find_get_context(pid, cpu);
if (IS_ERR(ctx))
return PTR_ERR(ctx);
ret = -ENOMEM;
counter = perf_counter_alloc(&event, cpu, record_type);
if (!counter)
goto err_put_context;
ret = hw_perf_counter_init(counter);
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);