Commit-ID: 26c86da8821f7b64fced498674990318bc34c8de
Gitweb: http://git.kernel.org/tip/26c86da8821f7b64fced498674990318bc34c8de
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Thu, 31 Oct 2013 10:19:59 +0100
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 6 Nov 2013 12:34:18 +0100
perf: Simplify the ring-buffer code
By using CIRC_SPACE() we can obviate the need for perf_output_space().
Shrinks the size of perf_output_begin() by 17 bytes on
x86_64-defconfig.
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
Cc: Michael Ellerman <michael@xxxxxxxxxxxxxx>
Cc: Michael Neuling <mikey@xxxxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: james.hogan@xxxxxxxxxx
Cc: Vince Weaver <vince@xxxxxxxxxx>
Cc: Victor Kaplansky <VICTORK@xxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Anton Blanchard <anton@xxxxxxxxx>
Link: http://lkml.kernel.org/n/tip-vtb0xb0llebmsdlfn1v5vtfj@xxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/events/ring_buffer.c | 37 ++++---------------------------------
1 file changed, 4 insertions(+), 33 deletions(-)
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 9c2ddfb..6929c58 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -12,40 +12,10 @@
#include <linux/perf_event.h>
#include <linux/vmalloc.h>
#include <linux/slab.h>
+#include <linux/circ_buf.h>
#include "internal.h"
-static bool perf_output_space(struct ring_buffer *rb, unsigned long tail,
- unsigned long offset, unsigned long head)
-{
- unsigned long sz = perf_data_size(rb);
- unsigned long mask = sz - 1;
-
- /*
- * check if user-writable
- * overwrite : over-write its own tail
- * !overwrite: buffer possibly drops events.
- */
- if (rb->overwrite)
- return true;
-
- /*
- * verify that payload is not bigger than buffer
- * otherwise masking logic may fail to detect
- * the "not enough space" condition
- */
- if ((head - offset) > sz)
- return false;
-
- offset = (offset - tail) & mask;
- head = (head - tail) & mask;
-
- if ((int)(head - offset) < 0)
- return false;
-
- return true;
-}
-
static void perf_output_wakeup(struct perf_output_handle *handle)
{
atomic_set(&handle->rb->poll, POLL_IN);
@@ -181,9 +151,10 @@ int perf_output_begin(struct perf_output_handle *handle,
tail = ACCESS_ONCE(rb->user_page->data_tail);
smp_mb();
offset = head = local_read(&rb->head);
- head += size;
- if (unlikely(!perf_output_space(rb, tail, offset, head)))
+ if (!rb->overwrite &&
+ unlikely(CIRC_SPACE(head, tail, perf_data_size(rb)) < size))
goto fail;
+ head += size;
} while (local_cmpxchg(&rb->head, offset, head) != offset);
if (head - local_read(&rb->wakeup) > rb->watermark)
--
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