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ring-buffer: try to discard unneeded timestamps

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There are times that a race may happen that we add a timestamp in a
nested write. This timestamp would just contain a zero delta and serves
no purpose.

Now that we have a way to discard events, this patch will try to discard
the timestamp instead of just wasting the space in the ring buffer.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt 2009-06-02 23:00:53 -04:00 committed by Steven Rostedt
parent a202355640
commit edd813bffc
1 changed files with 41 additions and 26 deletions
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67
kernel/trace/ring_buffer.c
View file

@ -1335,6 +1335,38 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
return event;
}
static inline int
rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer,
struct ring_buffer_event *event)
{
unsigned long new_index, old_index;
struct buffer_page *bpage;
unsigned long index;
unsigned long addr;
new_index = rb_event_index(event);
old_index = new_index + rb_event_length(event);
addr = (unsigned long)event;
addr &= PAGE_MASK;
bpage = cpu_buffer->tail_page;
if (bpage->page == (void *)addr && rb_page_write(bpage) == old_index) {
/*
* This is on the tail page. It is possible that
* a write could come in and move the tail page
* and write to the next page. That is fine
* because we just shorten what is on this page.
*/
index = local_cmpxchg(&bpage->write, old_index, new_index);
if (index == old_index)
return 1;
}
/* could not discard */
return 0;
}
static int
rb_add_time_stamp(struct ring_buffer_per_cpu *cpu_buffer,
u64 *ts, u64 *delta)
@ -1384,10 +1416,13 @@ rb_add_time_stamp(struct ring_buffer_per_cpu *cpu_buffer,
/* let the caller know this was the commit */
ret = 1;
} else {
/* Darn, this is just wasted space */
event->time_delta = 0;
event->array[0] = 0;
ret = 0;
/* Try to discard the event */
if (!rb_try_to_discard(cpu_buffer, event)) {
/* Darn, this is just wasted space */
event->time_delta = 0;
event->array[0] = 0;
ret = 0;
}
}
*delta = 0;
@ -1682,10 +1717,6 @@ void ring_buffer_discard_commit(struct ring_buffer *buffer,
struct ring_buffer_event *event)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long new_index, old_index;
struct buffer_page *bpage;
unsigned long index;
unsigned long addr;
int cpu;
/* The event is discarded regardless */
@ -1701,24 +1732,8 @@ void ring_buffer_discard_commit(struct ring_buffer *buffer,
cpu = smp_processor_id();
cpu_buffer = buffer->buffers[cpu];
new_index = rb_event_index(event);
old_index = new_index + rb_event_length(event);
addr = (unsigned long)event;
addr &= PAGE_MASK;
bpage = cpu_buffer->tail_page;
if (bpage->page == (void *)addr && rb_page_write(bpage) == old_index) {
/*
* This is on the tail page. It is possible that
* a write could come in and move the tail page
* and write to the next page. That is fine
* because we just shorten what is on this page.
*/
index = local_cmpxchg(&bpage->write, old_index, new_index);
if (index == old_index)
goto out;
}
if (!rb_try_to_discard(cpu_buffer, event))
goto out;
/*
* The commit is still visible by the reader, so we