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Commit 43a21ea8 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
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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: default avatarPeter 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: default avatarIngo Molnar <mingo@elte.hu>
parent d3a9262e

include/linux/perf_counter.h

+28 −12
Original line number Diff line number Diff line
@@ -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];

kernel/perf_counter.c

+130 −55
Original line number Diff line number Diff line
@@ -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);
@@ -2258,12 +2310,57 @@ out: 
	local_irq_restore(handle->flags);

}



static void perf_output_copy(struct perf_output_handle *handle,

			     const void *buf, unsigned int len)

{

	unsigned int pages_mask;

	unsigned int offset;

	unsigned int size;

	void **pages;



	offset		= handle->offset;

	pages_mask	= handle->data->nr_pages - 1;

	pages		= handle->data->data_pages;



	do {

		unsigned int page_offset;

		int nr;



		nr	    = (offset >> PAGE_SHIFT) & pages_mask;

		page_offset = offset & (PAGE_SIZE - 1);

		size	    = min_t(unsigned int, PAGE_SIZE - page_offset, len);



		memcpy(pages[nr] + page_offset, buf, size);



		len	    -= size;

		buf	    += size;

		offset	    += size;

	} while (len);



	handle->offset = offset;



	/*

	 * Check we didn't copy past our reservation window, taking the

	 * possible unsigned int wrap into account.

	 */

	WARN_ON_ONCE(((long)(handle->head - handle->offset)) < 0);

}



#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 overflow)

			     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.
@@ -2279,16 +2376,22 @@ static int perf_output_begin(struct perf_output_handle *handle, 
	handle->data	= data;

	handle->counter	= counter;

	handle->nmi	= nmi;

	handle->overflow = overflow;

	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;
@@ -2297,55 +2400,27 @@ static int perf_output_begin(struct perf_output_handle *handle, 
	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:

	perf_output_wakeup(handle);

	atomic_inc(&data->lost);

	perf_output_unlock(handle);

out:

	rcu_read_unlock();



	return -ENOSPC;

}



static void perf_output_copy(struct perf_output_handle *handle,

			     const void *buf, unsigned int len)

{

	unsigned int pages_mask;

	unsigned int offset;

	unsigned int size;

	void **pages;



	offset		= handle->offset;

	pages_mask	= handle->data->nr_pages - 1;

	pages		= handle->data->data_pages;



	do {

		unsigned int page_offset;

		int nr;



		nr	    = (offset >> PAGE_SHIFT) & pages_mask;

		page_offset = offset & (PAGE_SIZE - 1);

		size	    = min_t(unsigned int, PAGE_SIZE - page_offset, len);



		memcpy(pages[nr] + page_offset, buf, size);



		len	    -= size;

		buf	    += size;

		offset	    += size;

	} while (len);



	handle->offset = offset;



	/*

	 * Check we didn't copy past our reservation window, taking the

	 * possible unsigned int wrap into account.

	 */

	WARN_ON_ONCE(((long)(handle->head - handle->offset)) < 0);

}



#define perf_output_put(handle, x) \

	perf_output_copy((handle), &(x), sizeof(x))



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,