1/*
2 * CDDL HEADER START
3 *
4 * The contents of this file are subject to the terms of the
5 * Common Development and Distribution License (the "License").
6 * You may not use this file except in compliance with the License.
7 *
8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9 * or http://www.opensolaris.org/os/licensing.
10 * See the License for the specific language governing permissions
11 * and limitations under the License.
12 *
13 * When distributing Covered Code, include this CDDL HEADER in each
14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15 * If applicable, add the following below this CDDL HEADER, with the
16 * fields enclosed by brackets "[]" replaced with your own identifying
17 * information: Portions Copyright [yyyy] [name of copyright owner]
18 *
19 * CDDL HEADER END
20 */
21/*
22 * Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
23 */
24
25	.file	"smt_pause.s"
26
27#include <sys/asm_linkage.h>
28#include <../assym.h>
29#include <sys/stack.h>
30
31/*
32 * void smt_pause(void)
33 *
34 * Do nothing efficiently.
35 * We do the dance with the lwpid so that the actual address is spread
36 * across cache banks thus avoiding hot spots.
37 * Casx arguments are a no-op, but they force access to L2 cache, which
38 * takes lots of cycles.
39 */
40
41#ifdef lint
42void
43smt_pause(void)
44{
45}
46#else
47#define	BANKS	(4 * 64)	/* covers 4 cachelines, all banks */
48	ENTRY(smt_pause)
49	save	%sp, -SA(MINFRAME+BANKS), %sp
50	ld      [%g7 + UL_LWPID], %i5
51	add	%fp, STACK_BIAS-BANKS, %i3
52	and     %i5, 0x3, %i4           ! save last 2 bits
53	sll     %i4, 0x6, %i2           ! pick a slot
54	add     %i2, %i3, %o0
55	casx    [%o0], %g0, %g0
56	casx    [%o0], %g0, %g0
57	ret
58	restore
59	SET_SIZE(smt_pause)
60#endif
61