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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: Slava Pestov <slavapestov@google.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Slava Pestov 2011-07-15 14:23:58 -07:00 committed by Steven Rostedt
parent f43c738bfa
commit 884bfe89a4
3 changed files with 39 additions and 6 deletions
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1
include/linux/ring_buffer.h
View File

@ -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,

41
kernel/trace/ring_buffer.c
View File

@ -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);

3
kernel/trace/trace.c
View File

@ -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);