perf_counter: Add event overlow handling
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>
diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index a7d3a61..0765e8e 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -236,10 +236,16 @@
/*
* 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)
@@ -275,6 +281,15 @@
/*
* struct {
+ * struct perf_event_header header;
+ * u64 id;
+ * u64 lost;
+ * };
+ */
+ PERF_EVENT_LOST = 2,
+
+ /*
+ * struct {
* struct perf_event_header header;
*
* u32 pid, tid;
@@ -313,26 +328,26 @@
/*
* 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 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 @@
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];
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 109a957..7e9108e 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -1794,6 +1794,12 @@
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 @@
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 @@
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 @@
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 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 @@
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 @@
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 @@
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 @@
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 @@
#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 @@
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 @@
}
/*
- * Generic counter overflow handling.
+ * Generic counter overflow handling, sampling.
*/
int perf_counter_overflow(struct perf_counter *counter, int nmi,