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ring-buffer/tracing: Have iterator acknowledge dropped events 

Have the ring_buffer_iterator set a flag if events were dropped as it were
to go and peek at the next event. Have the trace file display this fact if
it happened with a "LOST EVENTS" message.

Link: http://lkml.kernel.org/r/20200317213417.045858900@goodmis.org

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
alistair/sensors
Steven Rostedt (VMware) 2020-03-17 17:32:32 -04:00
parent 06e0a548ba
commit c9b7a4a72f
3 changed files with 29 additions and 4 deletions
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1
include/linux/ring_buffer.h
View File

@ -138,6 +138,7 @@ ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts);
void ring_buffer_iter_advance(struct ring_buffer_iter *iter);
void ring_buffer_iter_reset(struct ring_buffer_iter *iter);
int ring_buffer_iter_empty(struct ring_buffer_iter *iter);
bool ring_buffer_iter_dropped(struct ring_buffer_iter *iter);
unsigned long ring_buffer_size(struct trace_buffer *buffer, int cpu);

16
kernel/trace/ring_buffer.c
View File

@ -510,6 +510,7 @@ struct ring_buffer_iter {
u64 read_stamp;
u64 page_stamp;
struct ring_buffer_event *event;
int missed_events;
};
/**
@ -1988,6 +1989,7 @@ rb_iter_head_event(struct ring_buffer_iter *iter)
iter->page_stamp = iter->read_stamp = iter->head_page->page->time_stamp;
iter->head = 0;
iter->next_event = 0;
iter->missed_events = 1;
return NULL;
}
@ -4191,6 +4193,20 @@ ring_buffer_peek(struct trace_buffer *buffer, int cpu, u64 *ts,
return event;
}
/** ring_buffer_iter_dropped - report if there are dropped events
* @iter: The ring buffer iterator
*
* Returns true if there was dropped events since the last peek.
*/
bool ring_buffer_iter_dropped(struct ring_buffer_iter *iter)
{
bool ret = iter->missed_events != 0;
iter->missed_events = 0;
return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_iter_dropped);
/**
* ring_buffer_iter_peek - peek at the next event to be read
* @iter: The ring buffer iterator

16
kernel/trace/trace.c
View File

@ -3388,11 +3388,15 @@ peek_next_entry(struct trace_iterator *iter, int cpu, u64 *ts,
struct ring_buffer_event *event;
struct ring_buffer_iter *buf_iter = trace_buffer_iter(iter, cpu);
if (buf_iter)
if (buf_iter) {
event = ring_buffer_iter_peek(buf_iter, ts);
else
if (lost_events)
*lost_events = ring_buffer_iter_dropped(buf_iter) ?
(unsigned long)-1 : 0;
} else {
event = ring_buffer_peek(iter->array_buffer->buffer, cpu, ts,
lost_events);
}
if (event) {
iter->ent_size = ring_buffer_event_length(event);
@ -4005,8 +4009,12 @@ enum print_line_t print_trace_line(struct trace_iterator *iter)
enum print_line_t ret;
if (iter->lost_events) {
trace_seq_printf(&iter->seq, "CPU:%d [LOST %lu EVENTS]\n",
iter->cpu, iter->lost_events);
if (iter->lost_events == (unsigned long)-1)
trace_seq_printf(&iter->seq, "CPU:%d [LOST EVENTS]\n",
iter->cpu);
else
trace_seq_printf(&iter->seq, "CPU:%d [LOST %lu EVENTS]\n",
iter->cpu, iter->lost_events);
if (trace_seq_has_overflowed(&iter->seq))
return TRACE_TYPE_PARTIAL_LINE;
}