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Commit 26c86da8 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

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: default avatarPeter 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: default avatarIngo Molnar <mingo@kernel.org>
parent 83bf9702

kernel/events/ring_buffer.c

+4 −33
Original line number Diff line number Diff line
@@ -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)