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author | Steven Rostedt <srostedt@redhat.com> | 2009-06-02 23:00:53 -0400 |
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committer | Steven Rostedt <rostedt@goodmis.org> | 2009-06-03 10:15:22 -0400 |
commit | edd813bffc62a980bb4fb9b1243f31c1cce78da3 (patch) | |
tree | 45dd8b0ca7b74f05bd545a1c3c7c4d2137f1b1d0 /kernel/trace/ring_buffer.c | |
parent | a2023556409cf7fec5d67a26f7fcfa57c5a4086d (diff) | |
download | kernel_samsung_tuna-edd813bffc62a980bb4fb9b1243f31c1cce78da3.zip kernel_samsung_tuna-edd813bffc62a980bb4fb9b1243f31c1cce78da3.tar.gz kernel_samsung_tuna-edd813bffc62a980bb4fb9b1243f31c1cce78da3.tar.bz2 |
ring-buffer: try to discard unneeded timestamps
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>
Diffstat (limited to 'kernel/trace/ring_buffer.c')
-rw-r--r-- | kernel/trace/ring_buffer.c | 67 |
1 files changed, 41 insertions, 26 deletions
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 9453023..5092660 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -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 |