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Message-ID: <4A528851.5040204@am.sony.com>
Date: Mon, 6 Jul 2009 16:27:13 -0700
From: Tim Bird <tim.bird@...sony.com>
To: Steven Rostedt <rostedt@...dmis.org>,
Frederic Weisbecker <fweisbec@...il.com>,
Ingo Molnar <mingo@...e.hu>,
linux kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH 2/2] ftrace: optimize duration filter event discard
Add a routine to allow optimizing the removal of the last
committed entry in the trace log. This is useful for
function duration tracing, and can greatly expand the
time coverage of a trace, by reclaiming almost all space
for filtered function events.
Please review the FIXTHIS lines, and let me know if
better concurrency control is needed here.
Signed-off-by: Tim Bird <tim.bird@...sony.com>
---
include/linux/ring_buffer.h | 8 +++++++
kernel/trace/ring_buffer.c | 45 ++++++++++++++++++++++++++++++++++++++++++++
kernel/trace/trace.c | 2 -
3 files changed, 54 insertions(+), 1 deletion(-)
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -106,6 +106,14 @@ void ring_buffer_discard_commit(struct r
struct ring_buffer_event *event);
/*
+ * ring_buffer_rewind_tail will remove an event that has already
+ * been committed. It remains to be determined if it is safe to
+ * do this.
+ */
+void ring_buffer_rewind_tail(struct ring_buffer *buffer,
+ struct ring_buffer_event *event);
+
+/*
* size is in bytes for each per CPU buffer.
*/
struct ring_buffer *
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1801,6 +1801,51 @@ void ring_buffer_discard_commit(struct r
EXPORT_SYMBOL_GPL(ring_buffer_discard_commit);
/**
+ * ring_buffer_rewind_tail - discard an event that was previously committed
+ * @buffer: the ring buffer
+ * @event: committed event to discard
+ *
+ * This is similar to ring_buffer_discard_commit but is intended to be
+ * performed on an event that has already been committed.
+ * This routine will try to free the event from the ring buffer.
+ *
+ * If there is some problem, the event is discarded, but not freed.
+ */
+void ring_buffer_rewind_tail(struct ring_buffer *buffer,
+ struct ring_buffer_event *event)
+{
+ struct ring_buffer_per_cpu *cpu_buffer;
+ int cpu;
+
+ /* The event is discarded regardless */
+ rb_event_discard(event);
+
+ cpu = smp_processor_id();
+ cpu_buffer = buffer->buffers[cpu];
+
+ /*
+ * If this is the last event in the buffer,
+ * this should work...
+ */
+ if (likely(rb_try_to_discard(cpu_buffer, event))) {
+ /* FIXTHIS - possibility for a race with a reader here? */
+
+ /* reduce the count of entries in the buffer */
+ local_dec(&cpu_buffer->entries);
+
+ /* FIXTHIS - possibility for a race with a writer here? */
+ rb_set_commit_to_write(cpu_buffer);
+
+ /*
+ * if a write comes in, between the try_to_discard() and
+ * the set_commit_to_write(), but was not committed yet,
+ * we just committed it. This should be rare.
+ */
+ }
+}
+EXPORT_SYMBOL_GPL(ring_buffer_rewind_tail);
+
+/**
* ring_buffer_write - write data to the buffer without reserving
* @buffer: The ring buffer to write to.
* @length: The length of the data being written (excluding the event header)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -999,7 +999,7 @@ static void trace_buffer_discard_func_en
prev_entry = ring_buffer_event_data(prev_event);
if (func == prev_entry->graph_ent.func) {
- ring_buffer_event_discard(prev_event);
+ ring_buffer_rewind_tail(global_trace.buffer, prev_event);
}
}
--
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