[PATCH v3 02/23] perf: Add AUX area to ring buffer for raw data streams

Alexander Shishkin
2014-08-11T05:24:47Z

From: Peter Zijlstra <peterz@infradead.org>

This patch introduces "AUX space" in the perf mmap buffer, intended for
exporting high bandwidth data streams to userspace, such as instruction
flow traces.

AUX space is a ring buffer, defined by aux_{offset,size} fields in the
user_page structure, and read/write pointers aux_{head,tail}, which abide
by the same rules as data_* counterparts of the main perf buffer.

In order to allocate/mmap AUX, userspace needs to set up aux_offset to
such an offset that will be greater than data_offset+data_size and
aux_size to be the desired buffer size. Both need to be page aligned.
Then, same aux_offset and aux_size should be passed to mmap() call and
if everything adds up, you should have an AUX buffer as a result.

Pages that are mapped into this buffer also come out of user's mlock
rlimit plus perf_event_mlock_kb allowance.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
---
include/linux/perf_event.h | 17 +++++
include/uapi/linux/perf_event.h | 16 +++++
kernel/events/core.c | 140 +++++++++++++++++++++++++++++++++-------
kernel/events/internal.h | 21 ++++++
kernel/events/ring_buffer.c | 86 ++++++++++++++++++++++--
5 files changed, 251 insertions(+), 29 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 707617a8c0..cf62338421 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -262,6 +262,18 @@ struct pmu {
* flush branch stack on context-switches (needed in cpu-wide mode)
*/
void (*flush_branch_stack) (void);
+
+ /*
+ * Set up pmu-private data structures for an AUX area
+ */
+ void *(*setup_aux) (int cpu, void **pages,
+ int nr_pages, bool overwrite);
+ /* optional */
+
+ /*
+ * Free pmu-private AUX data structures
+ */
+ void (*free_aux) (void *aux); /* optional */
};

/**
@@ -770,6 +782,11 @@ static inline bool has_branch_stack(struct perf_event *event)
return event->attr.sample_type & PERF_SAMPLE_BRANCH_STACK;
}

+static inline bool has_aux(struct perf_event *event)
+{
+ return event->pmu->setup_aux;
+}
+
extern int perf_output_begin(struct perf_output_handle *handle,
struct perf_event *event, unsigned int size);
extern void perf_output_end(struct perf_output_handle *handle);
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index f7d18c2cb7..7e0967c0f5 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -497,6 +497,22 @@ struct perf_event_mmap_page {
__u64 data_tail; /* user-space written tail */
__u64 data_offset; /* where the buffer starts */
__u64 data_size; /* data buffer size */
+
+ /*
+ * AUX area is defined by aux_{offset,size} fields that should be set
+ * by the userspace, so that
+ *
+ * aux_offset >= data_offset + data_size
+ *
+ * prior to mmap()ing it. Size of the mmap()ed area should be aux_size.
+ *
+ * Ring buffer pointers aux_{head,tail} have the same semantics as
+ * data_{head,tail} and same ordering rules apply.
+ */
+ __u64 aux_head;
+ __u64 aux_tail;
+ __u64 aux_offset;
+ __u64 aux_size;
};

#define PERF_RECORD_MISC_CPUMODE_MASK (7 << 0)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index bf58d40a26..c07768d0a0 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3979,6 +3979,8 @@ static void perf_mmap_open(struct vm_area_struct *vma)

atomic_inc(&event->mmap_count);
atomic_inc(&event->rb->mmap_count);
+ if (vma->vm_pgoff)
+ atomic_inc(&event->rb->aux_mmap_count);
}

/*
@@ -3998,6 +4000,20 @@ static void perf_mmap_close(struct vm_area_struct *vma)
int mmap_locked = rb->mmap_locked;
unsigned long size = perf_data_size(rb);

+ /*
+ * rb->aux_mmap_count will always drop before rb->mmap_count and
+ * event->mmap_count, so it is ok to use event->mmap_mutex to
+ * serialize with perf_mmap here.
+ */
+ if (rb_has_aux(rb) && vma->vm_pgoff == rb->aux_pgoff &&
+ atomic_dec_and_mutex_lock(&rb->aux_mmap_count, &event->mmap_mutex)) {
+ atomic_long_sub(rb->aux_nr_pages, &mmap_user->locked_vm);
+ vma->vm_mm->pinned_vm -= rb->aux_mmap_locked;
+
+ rb_free_aux(rb, event);
+ mutex_unlock(&event->mmap_mutex);
+ }
+
atomic_dec(&rb->mmap_count);

if (!atomic_dec_and_mutex_lock(&event->mmap_count, &event->mmap_mutex))
@@ -4071,7 +4087,7 @@ out_put:

static const struct vm_operations_struct perf_mmap_vmops = {
.open = perf_mmap_open,
- .close = perf_mmap_close,
+ .close = perf_mmap_close, /* non mergable */
.fault = perf_mmap_fault,
.page_mkwrite = perf_mmap_fault,
};
@@ -4082,10 +4098,10 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
unsigned long user_locked, user_lock_limit;
struct user_struct *user = current_user();
unsigned long locked, lock_limit;
- struct ring_buffer *rb;
+ struct ring_buffer *rb = NULL;
unsigned long vma_size;
unsigned long nr_pages;
- long user_extra, extra;
+ long user_extra = 0, extra = 0;
int ret = 0, flags = 0;

/*
@@ -4100,7 +4116,66 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
return -EINVAL;

vma_size = vma->vm_end - vma->vm_start;
- nr_pages = (vma_size / PAGE_SIZE) - 1;
+
+ if (vma->vm_pgoff == 0) {
+ nr_pages = (vma_size / PAGE_SIZE) - 1;
+ } else {
+ /*
+ * AUX area mapping: if rb->aux_nr_pages != 0, it's already
+ * mapped, all subsequent mappings should have the same size
+ * and offset. Must be above the normal perf buffer.
+ */
+ u64 aux_offset, aux_size;
+
+ if (!event->rb)
+ return -EINVAL;
+
+ nr_pages = vma_size / PAGE_SIZE;
+
+ mutex_lock(&event->mmap_mutex);
+ ret = -EINVAL;
+
+ rb = event->rb;
+ if (!rb)
+ goto aux_unlock;
+
+ aux_offset = ACCESS_ONCE(rb->user_page->aux_offset);
+ aux_size = ACCESS_ONCE(rb->user_page->aux_size);
+
+ if (aux_offset < perf_data_size(rb) + PAGE_SIZE)
+ goto aux_unlock;
+
+ if (aux_offset != vma->vm_pgoff << PAGE_SHIFT)
+ goto aux_unlock;
+
+ /* already mapped with a different offset */
+ if (rb_has_aux(rb) && rb->aux_pgoff != vma->vm_pgoff)
+ goto aux_unlock;
+
+ if (aux_size != vma_size || aux_size != nr_pages * PAGE_SIZE)
+ goto aux_unlock;
+
+ /* already mapped with a different size */
+ if (rb_has_aux(rb) && rb->aux_nr_pages != nr_pages)
+ goto aux_unlock;
+
+ if (!is_power_of_2(nr_pages))
+ goto aux_unlock;
+
+ if (!atomic_inc_not_zero(&rb->mmap_count))
+ goto aux_unlock;
+
+ if (rb_has_aux(rb)) {
+ atomic_inc(&rb->aux_mmap_count);
+ ret = 0;
+ goto unlock;
+ }
+
+ atomic_set(&rb->aux_mmap_count, 1);
+ user_extra = nr_pages;
+
+ goto accounting;
+ }

/*
* If we have rb pages ensure they're a power-of-two number, so we
@@ -4112,9 +4187,6 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
if (vma_size != PAGE_SIZE * (1 + nr_pages))
return -EINVAL;

- if (vma->vm_pgoff != 0)
- return -EINVAL;
-
WARN_ON_ONCE(event->ctx->parent_ctx);
again:
mutex_lock(&event->mmap_mutex);
@@ -4138,6 +4210,8 @@ again:
}

user_extra = nr_pages + 1;
+
+accounting:
user_lock_limit = sysctl_perf_event_mlock >> (PAGE_SHIFT - 10);

/*
@@ -4147,7 +4221,6 @@ again:

user_locked = atomic_long_read(&user->locked_vm) + user_extra;

- extra = 0;
if (user_locked > user_lock_limit)
extra = user_locked - user_lock_limit;

@@ -4161,35 +4234,45 @@ again:
goto unlock;
}

- WARN_ON(event->rb);
+ WARN_ON(!rb && event->rb);

if (vma->vm_flags & VM_WRITE)
flags |= RING_BUFFER_WRITABLE;

- rb = rb_alloc(nr_pages,
- event->attr.watermark ? event->attr.wakeup_watermark : 0,
- event->cpu, flags);
-
if (!rb) {
- ret = -ENOMEM;
- goto unlock;
- }
+ rb = rb_alloc(nr_pages,
+ event->attr.watermark ? event->attr.wakeup_watermark : 0,
+ event->cpu, flags);

- atomic_set(&rb->mmap_count, 1);
- rb->mmap_locked = extra;
- rb->mmap_user = get_current_user();
+ if (!rb) {
+ ret = -ENOMEM;
+ goto unlock;
+ }

- atomic_long_add(user_extra, &user->locked_vm);
- vma->vm_mm->pinned_vm += extra;
+ atomic_set(&rb->mmap_count, 1);
+ rb->mmap_user = get_current_user();
+ rb->mmap_locked = extra;

- ring_buffer_attach(event, rb);
+ ring_buffer_attach(event, rb);

- perf_event_init_userpage(event);
- perf_event_update_userpage(event);
+ perf_event_init_userpage(event);
+ perf_event_update_userpage(event);
+ } else {
+ ret = rb_alloc_aux(rb, event, vma->vm_pgoff, nr_pages, flags);
+ if (ret)
+ atomic_dec(&rb->mmap_count);
+ else
+ rb->aux_mmap_locked = extra;
+ }

unlock:
- if (!ret)
+ if (!ret) {
+ atomic_long_add(user_extra, &user->locked_vm);
+ vma->vm_mm->pinned_vm += extra;
+
atomic_inc(&event->mmap_count);
+ }
+aux_unlock:
mutex_unlock(&event->mmap_mutex);

/*
@@ -7036,6 +7119,13 @@ perf_event_set_output(struct perf_event *event, struct perf_event *output_event)
if (output_event->cpu == -1 && output_event->ctx != event->ctx)
goto out;

+ /*
+ * If both events generate aux data, they must be on the same PMU
+ */
+ if (has_aux(event) && has_aux(output_event) &&
+ event->pmu != output_event->pmu)
+ goto out;
+
set:
mutex_lock(&event->mmap_mutex);
/* Can't redirect output if we've got an active mmap() */
diff --git a/kernel/events/internal.h b/kernel/events/internal.h
index 569b218782..e5374030b1 100644
--- a/kernel/events/internal.h
+++ b/kernel/events/internal.h
@@ -35,6 +35,14 @@ struct ring_buffer {
unsigned long mmap_locked;
struct user_struct *mmap_user;

+ /* AUX area */
+ unsigned long aux_pgoff;
+ int aux_nr_pages;
+ atomic_t aux_mmap_count;
+ unsigned long aux_mmap_locked;
+ void **aux_pages;
+ void *aux_priv;
+
struct perf_event_mmap_page *user_page;
void *data_pages[0];
};
@@ -43,6 +51,14 @@ extern void rb_free(struct ring_buffer *rb);
extern struct ring_buffer *
rb_alloc(int nr_pages, long watermark, int cpu, int flags);
extern void perf_event_wakeup(struct perf_event *event);
+extern int rb_alloc_aux(struct ring_buffer *rb, struct perf_event *event,
+ pgoff_t pgoff, int nr_pages, int flags);
+extern void rb_free_aux(struct ring_buffer *rb, struct perf_event *event);
+
+static inline bool rb_has_aux(struct ring_buffer *rb)
+{
+ return !!rb->aux_nr_pages;
+}

extern void
perf_event_header__init_id(struct perf_event_header *header,
@@ -81,6 +97,11 @@ static inline unsigned long perf_data_size(struct ring_buffer *rb)
return rb->nr_pages << (PAGE_SHIFT + page_order(rb));
}

+static inline unsigned long perf_aux_size(struct ring_buffer *rb)
+{
+ return rb->aux_nr_pages << PAGE_SHIFT;
+}
+
#define DEFINE_OUTPUT_COPY(func_name, memcpy_func) \
static inline unsigned long \
func_name(struct perf_output_handle *handle, \
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 146a5792b1..00708d5916 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -242,14 +242,76 @@ ring_buffer_init(struct ring_buffer *rb, long watermark, int flags)
spin_lock_init(&rb->event_lock);
}

+int rb_alloc_aux(struct ring_buffer *rb, struct perf_event *event,
+ pgoff_t pgoff, int nr_pages, int flags)
+{
+ bool overwrite = !(flags & RING_BUFFER_WRITABLE);
+ int node = (event->cpu == -1) ? -1 : cpu_to_node(event->cpu);
+ int ret = -ENOMEM;
+
+ if (!has_aux(event))
+ return -ENOTSUPP;
+
+ rb->aux_pages = kzalloc_node(nr_pages * sizeof(void *), GFP_KERNEL, node);
+ if (!rb->aux_pages)
+ return -ENOMEM;
+
+ for (rb->aux_nr_pages = 0; rb->aux_nr_pages < nr_pages;
+ rb->aux_nr_pages++) {
+ struct page *page;
+
+ page = alloc_pages_node(node, GFP_KERNEL | __GFP_ZERO, 0);
+ if (!page)
+ goto out;
+
+ rb->aux_pages[rb->aux_nr_pages] = page_address(page);
+ }
+
+ rb->aux_priv = event->pmu->setup_aux(event->cpu, rb->aux_pages, nr_pages,
+ overwrite);
+ if (rb->aux_priv)
+ ret = 0;
+
+out:
+ if (!ret)
+ rb->aux_pgoff = pgoff;
+ else
+ rb_free_aux(rb, event);
+
+ return ret;
+}
+
+void rb_free_aux(struct ring_buffer *rb, struct perf_event *event)
+{
+ struct perf_event *iter;
+ int pg;
+
+ if (rb->aux_priv) {
+ /* disable all potential writers before freeing */
+ rcu_read_lock();
+ list_for_each_entry_rcu(iter, &rb->event_list, rb_entry)
+ perf_event_disable(iter);
+ rcu_read_unlock();
+
+ event->pmu->free_aux(rb->aux_priv);
+ rb->aux_priv = NULL;
+ }
+
+ for (pg = 0; pg < rb->aux_nr_pages; pg++)
+ free_page((unsigned long)rb->aux_pages[pg]);
+
+ kfree(rb->aux_pages);
+ rb->aux_nr_pages = 0;
+}
+
#ifndef CONFIG_PERF_USE_VMALLOC

/*
* Back perf_mmap() with regular GFP_KERNEL-0 pages.
*/

-struct page *
-perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
+static struct page *
+__perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
{
if (pgoff > rb->nr_pages)
return NULL;
@@ -339,8 +401,8 @@ static int data_page_nr(struct ring_buffer *rb)
return rb->nr_pages << page_order(rb);
}

-struct page *
-perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
+static struct page *
+__perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
{
/* The '>' counts in the user page. */
if (pgoff > data_page_nr(rb))
@@ -415,3 +477,19 @@ fail:
}

#endif
+
+struct page *
+perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
+{
+ if (rb->aux_nr_pages) {
+ /* above AUX space */
+ if (pgoff > rb->aux_pgoff + rb->aux_nr_pages)
+ return NULL;
+
+ /* AUX space */
+ if (pgoff >= rb->aux_pgoff)
+ return virt_to_page(rb->aux_pages[pgoff - rb->aux_pgoff]);
+ }
+
+ return __perf_mmap_to_page(rb, pgoff);
+}
--
2.1.0.rc1