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Commit 884bfe89 authored by Slava Pestov's avatar Slava Pestov Committed by Steven Rostedt
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ring-buffer: Add a 'dropped events' counter 

The existing 'overrun' counter is incremented when the ring
buffer wraps around, with overflow on (the default). We wanted
a way to count requests lost from the buffer filling up with
overflow off, too. I decided to add a new counter instead
of retro-fitting the existing one because it seems like a
different statistic to count conceptually, and also because
of how the code was structured.

Link: http://lkml.kernel.org/r/1310765038-26399-1-git-send-email-slavapestov@google.com



Signed-off-by: default avatarSlava Pestov <slavapestov@google.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent f43c738b

include/linux/ring_buffer.h

+1 −0
Original line number Diff line number Diff line
@@ -166,6 +166,7 @@ unsigned long ring_buffer_overruns(struct ring_buffer *buffer); 
unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu);

unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu);

unsigned long ring_buffer_commit_overrun_cpu(struct ring_buffer *buffer, int cpu);

unsigned long ring_buffer_dropped_events_cpu(struct ring_buffer *buffer, int cpu);



u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu);

void ring_buffer_normalize_time_stamp(struct ring_buffer *buffer,

kernel/trace/ring_buffer.c

+35 −6
Original line number Diff line number Diff line
@@ -460,9 +460,10 @@ struct ring_buffer_per_cpu { 
	unsigned long			lost_events;

	unsigned long			last_overrun;

	local_t				entries_bytes;

	local_t				commit_overrun;

	local_t				overrun;

	local_t				entries;

	local_t				overrun;

	local_t				commit_overrun;

	local_t				dropped_events;

	local_t				committing;

	local_t				commits;

	unsigned long			read;
@@ -2155,8 +2156,10 @@ rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer, 
			 * If we are not in overwrite mode,

			 * this is easy, just stop here.

			 */

			if (!(buffer->flags & RB_FL_OVERWRITE))

			if (!(buffer->flags & RB_FL_OVERWRITE)) {

				local_inc(&cpu_buffer->dropped_events);

				goto out_reset;

			}



			ret = rb_handle_head_page(cpu_buffer,

						  tail_page,
@@ -2995,7 +2998,8 @@ unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu) 
EXPORT_SYMBOL_GPL(ring_buffer_entries_cpu);



/**

 * ring_buffer_overrun_cpu - get the number of overruns in a cpu_buffer

 * ring_buffer_overrun_cpu - get the number of overruns caused by the ring

 * buffer wrapping around (only if RB_FL_OVERWRITE is on).

 * @buffer: The ring buffer

 * @cpu: The per CPU buffer to get the number of overruns from

 */
@@ -3015,7 +3019,9 @@ unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu) 
EXPORT_SYMBOL_GPL(ring_buffer_overrun_cpu);



/**

 * ring_buffer_commit_overrun_cpu - get the number of overruns caused by commits

 * ring_buffer_commit_overrun_cpu - get the number of overruns caused by

 * commits failing due to the buffer wrapping around while there are uncommitted

 * events, such as during an interrupt storm.

 * @buffer: The ring buffer

 * @cpu: The per CPU buffer to get the number of overruns from

 */
@@ -3035,6 +3041,28 @@ ring_buffer_commit_overrun_cpu(struct ring_buffer *buffer, int cpu) 
}

EXPORT_SYMBOL_GPL(ring_buffer_commit_overrun_cpu);



/**

 * ring_buffer_dropped_events_cpu - get the number of dropped events caused by

 * the ring buffer filling up (only if RB_FL_OVERWRITE is off).

 * @buffer: The ring buffer

 * @cpu: The per CPU buffer to get the number of overruns from

 */

unsigned long

ring_buffer_dropped_events_cpu(struct ring_buffer *buffer, int cpu)

{

	struct ring_buffer_per_cpu *cpu_buffer;

	unsigned long ret;



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

		return 0;



	cpu_buffer = buffer->buffers[cpu];

	ret = local_read(&cpu_buffer->dropped_events);



	return ret;

}

EXPORT_SYMBOL_GPL(ring_buffer_dropped_events_cpu);



/**

 * ring_buffer_entries - get the number of entries in a buffer

 * @buffer: The ring buffer
@@ -3864,9 +3892,10 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer) 
	local_set(&cpu_buffer->reader_page->page->commit, 0);

	cpu_buffer->reader_page->read = 0;



	local_set(&cpu_buffer->commit_overrun, 0);

	local_set(&cpu_buffer->entries_bytes, 0);

	local_set(&cpu_buffer->overrun, 0);

	local_set(&cpu_buffer->commit_overrun, 0);

	local_set(&cpu_buffer->dropped_events, 0);

	local_set(&cpu_buffer->entries, 0);

	local_set(&cpu_buffer->committing, 0);

	local_set(&cpu_buffer->commits, 0);

kernel/trace/trace.c

+3 −0
Original line number Diff line number Diff line
@@ -4385,6 +4385,9 @@ tracing_stats_read(struct file *filp, char __user *ubuf, 
	usec_rem = do_div(t, USEC_PER_SEC);

	trace_seq_printf(s, "now ts: %5llu.%06lu\n", t, usec_rem);



	cnt = ring_buffer_dropped_events_cpu(tr->buffer, cpu);

	trace_seq_printf(s, "dropped events: %ld\n", cnt);



	count = simple_read_from_buffer(ubuf, count, ppos, s->buffer, s->len);



	kfree(s);