6944589 need pause API

PSARC/2010/293 smt_pause

1 files changed, 60 insertions, 0 deletions

diff --git a/usr/src/lib/libc/sparc/gen/smt_pause.s b/usr/src/lib/libc/sparc/gen/smt_pause.s
new file mode 100644
index 0000000000..93739d0196
--- /dev/null
+++ b/usr/src/lib/libc/sparc/gen/smt_pause.s
@@ -0,0 +1,60 @@
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License (the "License").
+ * You may not use this file except in compliance with the License.
+ *
+ * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+ * or http://www.opensolaris.org/os/licensing.
+ * See the License for the specific language governing permissions
+ * and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+/*
+ * Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
+ */
+
+	.file	"smt_pause.s"
+
+#include <sys/asm_linkage.h>
+#include <../assym.h>
+#include <sys/stack.h>
+
+/*
+ * void smt_pause(void)
+ *
+ * Do nothing efficiently.
+ * We do the dance with the lwpid so that the actual address is spread
+ * across cache banks thus avoiding hot spots.
+ * Casx arguments are a no-op, but they force access to L2 cache, which
+ * takes lots of cycles.
+ */
+
+#ifdef lint
+void
+smt_pause(void)
+{
+}
+#else
+#define	BANKS	(4 * 64)	/* covers 4 cachelines, all banks */
+	ENTRY(smt_pause)
+	save	%sp, -SA(MINFRAME+BANKS), %sp
+	ld      [%g7 + UL_LWPID], %i5
+	add	%fp, STACK_BIAS-BANKS, %i3
+	and     %i5, 0x3, %i4           ! save last 2 bits
+	sll     %i4, 0x6, %i2           ! pick a slot
+	add     %i2, %i3, %o0
+	casx    [%o0], %g0, %g0
+	casx    [%o0], %g0, %g0
+	ret
+	restore
+	SET_SIZE(smt_pause)
+#endif