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Commit 2c2b0a78 authored by Steven Rostedt (VMware)'s avatar Steven Rostedt (VMware)
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ring-buffer: Add percentage of ring buffer full to wake up reader 



Instead of just waiting for a page to be full before waking up a pending
reader, allow the reader to pass in a "percentage" of pages that have
content before waking up a reader. This should help keep the process of
reading the events not cause wake ups that constantly cause reading of the
buffer.

Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 9c8e2f6d

include/linux/ring_buffer.h

+3 −1
Original line number Diff line number Diff line
@@ -97,7 +97,7 @@ __ring_buffer_alloc(unsigned long size, unsigned flags, struct lock_class_key *k 
	__ring_buffer_alloc((size), (flags), &__key);	\

})



int ring_buffer_wait(struct ring_buffer *buffer, int cpu, bool full);

int ring_buffer_wait(struct ring_buffer *buffer, int cpu, int full);

__poll_t ring_buffer_poll_wait(struct ring_buffer *buffer, int cpu,

			  struct file *filp, poll_table *poll_table);
@@ -189,6 +189,8 @@ bool ring_buffer_time_stamp_abs(struct ring_buffer *buffer); 


size_t ring_buffer_page_len(void *page);



size_t ring_buffer_nr_pages(struct ring_buffer *buffer, int cpu);

size_t ring_buffer_nr_dirty_pages(struct ring_buffer *buffer, int cpu);



void *ring_buffer_alloc_read_page(struct ring_buffer *buffer, int cpu);

void ring_buffer_free_read_page(struct ring_buffer *buffer, int cpu, void *data);

kernel/trace/ring_buffer.c

+66 −5
Original line number Diff line number Diff line
@@ -487,6 +487,9 @@ struct ring_buffer_per_cpu { 
	local_t				dropped_events;

	local_t				committing;

	local_t				commits;

	local_t				pages_touched;

	local_t				pages_read;

	size_t				shortest_full;

	unsigned long			read;

	unsigned long			read_bytes;

	u64				write_stamp;
@@ -529,6 +532,41 @@ struct ring_buffer_iter { 
	u64				read_stamp;

};



/**

 * ring_buffer_nr_pages - get the number of buffer pages in the ring buffer

 * @buffer: The ring_buffer to get the number of pages from

 * @cpu: The cpu of the ring_buffer to get the number of pages from

 *

 * Returns the number of pages used by a per_cpu buffer of the ring buffer.

 */

size_t ring_buffer_nr_pages(struct ring_buffer *buffer, int cpu)

{

	return buffer->buffers[cpu]->nr_pages;

}



/**

 * ring_buffer_nr_pages_dirty - get the number of used pages in the ring buffer

 * @buffer: The ring_buffer to get the number of pages from

 * @cpu: The cpu of the ring_buffer to get the number of pages from

 *

 * Returns the number of pages that have content in the ring buffer.

 */

size_t ring_buffer_nr_dirty_pages(struct ring_buffer *buffer, int cpu)

{

	size_t read;

	size_t cnt;



	read = local_read(&buffer->buffers[cpu]->pages_read);

	cnt = local_read(&buffer->buffers[cpu]->pages_touched);

	/* The reader can read an empty page, but not more than that */

	if (cnt < read) {

		WARN_ON_ONCE(read > cnt + 1);

		return 0;

	}



	return cnt - read;

}



/*

 * rb_wake_up_waiters - wake up tasks waiting for ring buffer input

 *
@@ -556,7 +594,7 @@ static void rb_wake_up_waiters(struct irq_work *work) 
 * as data is added to any of the @buffer's cpu buffers. Otherwise

 * it will wait for data to be added to a specific cpu buffer.

 */

int ring_buffer_wait(struct ring_buffer *buffer, int cpu, bool full)

int ring_buffer_wait(struct ring_buffer *buffer, int cpu, int full)

{

	struct ring_buffer_per_cpu *uninitialized_var(cpu_buffer);

	DEFINE_WAIT(wait);
@@ -571,7 +609,7 @@ int ring_buffer_wait(struct ring_buffer *buffer, int cpu, bool full) 
	if (cpu == RING_BUFFER_ALL_CPUS) {

		work = &buffer->irq_work;

		/* Full only makes sense on per cpu reads */

		full = false;

		full = 0;

	} else {

		if (!cpumask_test_cpu(cpu, buffer->cpumask))

			return -ENODEV;
@@ -623,15 +661,22 @@ int ring_buffer_wait(struct ring_buffer *buffer, int cpu, bool full) 
		    !ring_buffer_empty_cpu(buffer, cpu)) {

			unsigned long flags;

			bool pagebusy;

			size_t nr_pages;

			size_t dirty;



			if (!full)

				break;



			raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);

			pagebusy = cpu_buffer->reader_page == cpu_buffer->commit_page;

			nr_pages = cpu_buffer->nr_pages;

			dirty = ring_buffer_nr_dirty_pages(buffer, cpu);

			if (!cpu_buffer->shortest_full ||

			    cpu_buffer->shortest_full < full)

				cpu_buffer->shortest_full = full;

			raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);



			if (!pagebusy)

			if (!pagebusy &&

			    (!nr_pages || (dirty * 100) > full * nr_pages))

				break;

		}
@@ -1054,6 +1099,7 @@ static void rb_tail_page_update(struct ring_buffer_per_cpu *cpu_buffer, 
	old_write = local_add_return(RB_WRITE_INTCNT, &next_page->write);

	old_entries = local_add_return(RB_WRITE_INTCNT, &next_page->entries);



	local_inc(&cpu_buffer->pages_touched);

	/*

	 * Just make sure we have seen our old_write and synchronize

	 * with any interrupts that come in.
@@ -2603,6 +2649,16 @@ rb_wakeups(struct ring_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer) 
	pagebusy = cpu_buffer->reader_page == cpu_buffer->commit_page;



	if (!pagebusy && cpu_buffer->irq_work.full_waiters_pending) {

		size_t nr_pages;

		size_t dirty;

		size_t full;



		full = cpu_buffer->shortest_full;

		nr_pages = cpu_buffer->nr_pages;

		dirty = ring_buffer_nr_dirty_pages(buffer, cpu_buffer->cpu);

		if (full && nr_pages && (dirty * 100) <= full * nr_pages)

			return;



		cpu_buffer->irq_work.wakeup_full = true;

		cpu_buffer->irq_work.full_waiters_pending = false;

		/* irq_work_queue() supplies it's own memory barriers */
@@ -3732,13 +3788,15 @@ rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer) 
		goto spin;



	/*

	 * Yeah! We succeeded in replacing the page.

	 * Yay! We succeeded in replacing the page.

	 *

	 * Now make the new head point back to the reader page.

	 */

	rb_list_head(reader->list.next)->prev = &cpu_buffer->reader_page->list;

	rb_inc_page(cpu_buffer, &cpu_buffer->head_page);



	local_inc(&cpu_buffer->pages_read);



	/* Finally update the reader page to the new head */

	cpu_buffer->reader_page = reader;

	cpu_buffer->reader_page->read = 0;
@@ -4334,6 +4392,9 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer) 
	local_set(&cpu_buffer->entries, 0);

	local_set(&cpu_buffer->committing, 0);

	local_set(&cpu_buffer->commits, 0);

	local_set(&cpu_buffer->pages_touched, 0);

	local_set(&cpu_buffer->pages_read, 0);

	cpu_buffer->shortest_full = 0;

	cpu_buffer->read = 0;

	cpu_buffer->read_bytes = 0;

kernel/trace/trace.c

+4 −4
Original line number Diff line number Diff line
@@ -1431,7 +1431,7 @@ update_max_tr_single(struct trace_array *tr, struct task_struct *tsk, int cpu) 
}

#endif /* CONFIG_TRACER_MAX_TRACE */



static int wait_on_pipe(struct trace_iterator *iter, bool full)

static int wait_on_pipe(struct trace_iterator *iter, int full)

{

	/* Iterators are static, they should be filled or empty */

	if (trace_buffer_iter(iter, iter->cpu_file))
@@ -5693,7 +5693,7 @@ static int tracing_wait_pipe(struct file *filp) 


		mutex_unlock(&iter->mutex);



		ret = wait_on_pipe(iter, false);

		ret = wait_on_pipe(iter, 0);



		mutex_lock(&iter->mutex);
@@ -6751,7 +6751,7 @@ tracing_buffers_read(struct file *filp, char __user *ubuf, 
			if ((filp->f_flags & O_NONBLOCK))

				return -EAGAIN;



			ret = wait_on_pipe(iter, false);

			ret = wait_on_pipe(iter, 0);

			if (ret)

				return ret;
@@ -6948,7 +6948,7 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos, 
		if ((file->f_flags & O_NONBLOCK) || (flags & SPLICE_F_NONBLOCK))

			goto out;



		ret = wait_on_pipe(iter, true);

		ret = wait_on_pipe(iter, 1);

		if (ret)

			goto out;