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@infradead.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Michael Ellerman <michael@ellerman.id.au>
Cc: Michael Neuling <mikey@neuling.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: james.hogan@imgtec.com
Cc: Vince Weaver <vince@deater.net>
Cc: Victor Kaplansky <VICTORK@il.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Anton Blanchard <anton@samba.org>
Link: http://lkml.kernel.org/n/tip-vtb0xb0llebmsdlfn1v5vtfj@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 4 insertions, 33 deletions

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 9c2ddfbf4525..6929c5848d4f 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)