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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>
This commit is contained in:
Peter Zijlstra 2013-10-31 10:19:59 +01:00 committed by Ingo Molnar
parent 83bf9702c8
commit 26c86da882
1 changed files with 4 additions and 33 deletions
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37
kernel/events/ring_buffer.c
View File

@ -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)