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perf_counter: Add event overlow handling

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Alternative method of mmap() data output handling that provides
better overflow management and a more reliable data stream.

Unlike the previous method, that didn't have any user->kernel
feedback and relied on userspace keeping up, this method relies on
userspace writing its last read position into the control page.

It will ensure new output doesn't overwrite not-yet read events,
new events for which there is no space left are lost and the
overflow counter is incremented, providing exact event loss
numbers.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra
2009-03-25 19:39:37 +01:00
committed by Ingo Molnar
parent d3a9262e59
commit 43a21ea81a
2 changed files with 162 additions and 71 deletions
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193
kernel/perf_counter.c
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@@ -1794,6 +1794,12 @@ static int perf_mmap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
struct perf_mmap_data *data;
int ret = VM_FAULT_SIGBUS;
if (vmf->flags & FAULT_FLAG_MKWRITE) {
if (vmf->pgoff == 0)
ret = 0;
return ret;
}
rcu_read_lock();
data = rcu_dereference(counter->data);
if (!data)
@@ -1807,9 +1813,16 @@ static int perf_mmap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
if ((unsigned)nr > data->nr_pages)
goto unlock;
if (vmf->flags & FAULT_FLAG_WRITE)
goto unlock;
vmf->page = virt_to_page(data->data_pages[nr]);
}
get_page(vmf->page);
vmf->page->mapping = vma->vm_file->f_mapping;
vmf->page->index = vmf->pgoff;
ret = 0;
unlock:
rcu_read_unlock();
@@ -1862,6 +1875,14 @@ fail:
return -ENOMEM;
}
static void perf_mmap_free_page(unsigned long addr)
{
struct page *page = virt_to_page(addr);
page->mapping = NULL;
__free_page(page);
}
static void __perf_mmap_data_free(struct rcu_head *rcu_head)
{
struct perf_mmap_data *data;
@@ -1869,9 +1890,10 @@ static void __perf_mmap_data_free(struct rcu_head *rcu_head)
data = container_of(rcu_head, struct perf_mmap_data, rcu_head);
free_page((unsigned long)data->user_page);
perf_mmap_free_page((unsigned long)data->user_page);
for (i = 0; i < data->nr_pages; i++)
free_page((unsigned long)data->data_pages[i]);
perf_mmap_free_page((unsigned long)data->data_pages[i]);
kfree(data);
}
@@ -1908,9 +1930,10 @@ static void perf_mmap_close(struct vm_area_struct *vma)
}
static struct vm_operations_struct perf_mmap_vmops = {
.open = perf_mmap_open,
.close = perf_mmap_close,
.fault = perf_mmap_fault,
.open = perf_mmap_open,
.close = perf_mmap_close,
.fault = perf_mmap_fault,
.page_mkwrite = perf_mmap_fault,
};
static int perf_mmap(struct file *file, struct vm_area_struct *vma)
@@ -1924,7 +1947,7 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
long user_extra, extra;
int ret = 0;
if (!(vma->vm_flags & VM_SHARED) || (vma->vm_flags & VM_WRITE))
if (!(vma->vm_flags & VM_SHARED))
return -EINVAL;
vma_size = vma->vm_end - vma->vm_start;
@@ -1983,10 +2006,12 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
atomic_long_add(user_extra, &user->locked_vm);
vma->vm_mm->locked_vm += extra;
counter->data->nr_locked = extra;
if (vma->vm_flags & VM_WRITE)
counter->data->writable = 1;
unlock:
mutex_unlock(&counter->mmap_mutex);
vma->vm_flags &= ~VM_MAYWRITE;
vma->vm_flags |= VM_RESERVED;
vma->vm_ops = &perf_mmap_vmops;
@@ -2163,11 +2188,38 @@ struct perf_output_handle {
unsigned long head;
unsigned long offset;
int nmi;
int overflow;
int sample;
int locked;
unsigned long flags;
};
static bool perf_output_space(struct perf_mmap_data *data,
unsigned int offset, unsigned int head)
{
unsigned long tail;
unsigned long mask;
if (!data->writable)
return true;
mask = (data->nr_pages << PAGE_SHIFT) - 1;
/*
* Userspace could choose to issue a mb() before updating the tail
* pointer. So that all reads will be completed before the write is
* issued.
*/
tail = ACCESS_ONCE(data->user_page->data_tail);
smp_rmb();
offset = (offset - tail) & mask;
head = (head - tail) & mask;
if ((int)(head - offset) < 0)
return false;
return true;
}
static void perf_output_wakeup(struct perf_output_handle *handle)
{
atomic_set(&handle->data->poll, POLL_IN);
@@ -2258,55 +2310,6 @@ out:
local_irq_restore(handle->flags);
}
static int perf_output_begin(struct perf_output_handle *handle,
struct perf_counter *counter, unsigned int size,
int nmi, int overflow)
{
struct perf_mmap_data *data;
unsigned int offset, head;
/*
* For inherited counters we send all the output towards the parent.
*/
if (counter->parent)
counter = counter->parent;
rcu_read_lock();
data = rcu_dereference(counter->data);
if (!data)
goto out;
handle->data = data;
handle->counter = counter;
handle->nmi = nmi;
handle->overflow = overflow;
if (!data->nr_pages)
goto fail;
perf_output_lock(handle);
do {
offset = head = atomic_long_read(&data->head);
head += size;
} while (atomic_long_cmpxchg(&data->head, offset, head) != offset);
handle->offset = offset;
handle->head = head;
if ((offset >> PAGE_SHIFT) != (head >> PAGE_SHIFT))
atomic_set(&data->wakeup, 1);
return 0;
fail:
perf_output_wakeup(handle);
out:
rcu_read_unlock();
return -ENOSPC;
}
static void perf_output_copy(struct perf_output_handle *handle,
const void *buf, unsigned int len)
{
@@ -2346,6 +2349,78 @@ static void perf_output_copy(struct perf_output_handle *handle,
#define perf_output_put(handle, x) \
perf_output_copy((handle), &(x), sizeof(x))
static int perf_output_begin(struct perf_output_handle *handle,
struct perf_counter *counter, unsigned int size,
int nmi, int sample)
{
struct perf_mmap_data *data;
unsigned int offset, head;
int have_lost;
struct {
struct perf_event_header header;
u64 id;
u64 lost;
} lost_event;
/*
* For inherited counters we send all the output towards the parent.
*/
if (counter->parent)
counter = counter->parent;
rcu_read_lock();
data = rcu_dereference(counter->data);
if (!data)
goto out;
handle->data = data;
handle->counter = counter;
handle->nmi = nmi;
handle->sample = sample;
if (!data->nr_pages)
goto fail;
have_lost = atomic_read(&data->lost);
if (have_lost)
size += sizeof(lost_event);
perf_output_lock(handle);
do {
offset = head = atomic_long_read(&data->head);
head += size;
if (unlikely(!perf_output_space(data, offset, head)))
goto fail;
} while (atomic_long_cmpxchg(&data->head, offset, head) != offset);
handle->offset = offset;
handle->head = head;
if ((offset >> PAGE_SHIFT) != (head >> PAGE_SHIFT))
atomic_set(&data->wakeup, 1);
if (have_lost) {
lost_event.header.type = PERF_EVENT_LOST;
lost_event.header.misc = 0;
lost_event.header.size = sizeof(lost_event);
lost_event.id = counter->id;
lost_event.lost = atomic_xchg(&data->lost, 0);
perf_output_put(handle, lost_event);
}
return 0;
fail:
atomic_inc(&data->lost);
perf_output_unlock(handle);
out:
rcu_read_unlock();
return -ENOSPC;
}
static void perf_output_end(struct perf_output_handle *handle)
{
struct perf_counter *counter = handle->counter;
@@ -2353,7 +2428,7 @@ static void perf_output_end(struct perf_output_handle *handle)
int wakeup_events = counter->attr.wakeup_events;
if (handle->overflow && wakeup_events) {
if (handle->sample && wakeup_events) {
int events = atomic_inc_return(&data->events);
if (events >= wakeup_events) {
atomic_sub(wakeup_events, &data->events);
@@ -2958,7 +3033,7 @@ static void perf_log_throttle(struct perf_counter *counter, int enable)
}
/*
* Generic counter overflow handling.
* Generic counter overflow handling, sampling.
*/
int perf_counter_overflow(struct perf_counter *counter, int nmi,