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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
Show stats Download patch file Download diff file Expand all files Collapse all files

40
include/linux/perf_counter.h
View file

@ -236,10 +236,16 @@ struct perf_counter_mmap_page {
/*
* Control data for the mmap() data buffer.
*
* User-space reading this value should issue an rmb(), on SMP capable
* platforms, after reading this value -- see perf_counter_wakeup().
* User-space reading the @data_head value should issue an rmb(), on
* SMP capable platforms, after reading this value -- see
* perf_counter_wakeup().
*
* When the mapping is PROT_WRITE the @data_tail value should be
* written by userspace to reflect the last read data. In this case
* the kernel will not over-write unread data.
*/
__u64 data_head; /* head in the data section */
__u64 data_tail; /* user-space written tail */
};
#define PERF_EVENT_MISC_CPUMODE_MASK (3 << 0)
@ -273,6 +279,15 @@ enum perf_event_type {
*/
PERF_EVENT_MMAP = 1,
/*
* struct {
* struct perf_event_header header;
* u64 id;
* u64 lost;
* };
*/
PERF_EVENT_LOST = 2,
/*
* struct {
* struct perf_event_header header;
@ -313,26 +328,26 @@ enum perf_event_type {
/*
* When header.misc & PERF_EVENT_MISC_OVERFLOW the event_type field
* will be PERF_RECORD_*
* will be PERF_SAMPLE_*
*
* struct {
* struct perf_event_header header;
*
* { u64 ip; } && PERF_RECORD_IP
* { u32 pid, tid; } && PERF_RECORD_TID
* { u64 time; } && PERF_RECORD_TIME
* { u64 addr; } && PERF_RECORD_ADDR
* { u64 config; } && PERF_RECORD_CONFIG
* { u32 cpu, res; } && PERF_RECORD_CPU
* { u64 ip; } && PERF_SAMPLE_IP
* { u32 pid, tid; } && PERF_SAMPLE_TID
* { u64 time; } && PERF_SAMPLE_TIME
* { u64 addr; } && PERF_SAMPLE_ADDR
* { u64 config; } && PERF_SAMPLE_CONFIG
* { u32 cpu, res; } && PERF_SAMPLE_CPU
*
* { u64 nr;
* { u64 id, val; } cnt[nr]; } && PERF_RECORD_GROUP
* { u64 id, val; } cnt[nr]; } && PERF_SAMPLE_GROUP
*
* { u16 nr,
* hv,
* kernel,
* user;
* u64 ips[nr]; } && PERF_RECORD_CALLCHAIN
* u64 ips[nr]; } && PERF_SAMPLE_CALLCHAIN
* };
*/
};
@ -424,6 +439,7 @@ struct file;
struct perf_mmap_data {
struct rcu_head rcu_head;
int nr_pages; /* nr of data pages */
int writable; /* are we writable */
int nr_locked; /* nr pages mlocked */
atomic_t poll; /* POLL_ for wakeups */
@ -433,8 +449,8 @@ struct perf_mmap_data {
atomic_long_t done_head; /* completed head */
atomic_t lock; /* concurrent writes */
atomic_t wakeup; /* needs a wakeup */
atomic_t lost; /* nr records lost */
struct perf_counter_mmap_page *user_page;
void *data_pages[0];

187
kernel/perf_counter.c
View file

@ -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);
}
@ -1911,6 +1933,7 @@ static struct vm_operations_struct perf_mmap_vmops = {
.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,