X-Git-Url: http://git.liburcu.org/?a=blobdiff_plain;f=include%2Furcu%2Farch%2Fppc.h;h=1285b6d2211f3239b850a73f8a3fb277a3516990;hb=HEAD;hp=791529ebb1a08ff3db124103474522b77bf0ad15;hpb=6893800a4d1cc14dff0395ddcd660a5138db183d;p=urcu.git

diff --git a/include/urcu/arch/ppc.h b/include/urcu/arch/ppc.h
index 791529e..1285b6d 100644
--- a/include/urcu/arch/ppc.h
+++ b/include/urcu/arch/ppc.h
@@ -1,25 +1,13 @@
+// SPDX-FileCopyrightText: 2009 Paul E. McKenney, IBM Corporation.
+// SPDX-FileCopyrightText: 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+//
+// SPDX-License-Identifier: LGPL-2.1-or-later
+
 #ifndef _URCU_ARCH_PPC_H
 #define _URCU_ARCH_PPC_H
 
 /*
  * arch_ppc.h: trivial definitions for the powerpc architecture.
- *
- * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
- * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
- *
- * This library is free software; you can redistribute it and/or
- * modify it under the terms of the GNU Lesser General Public
- * License as published by the Free Software Foundation; either
- * version 2.1 of the License, or (at your option) any later version.
- *
- * This library is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
- * Lesser General Public License for more details.
- *
- * You should have received a copy of the GNU Lesser General Public
- * License along with this library; if not, write to the Free Software
- * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
 #include <urcu/compiler.h>
@@ -31,7 +19,30 @@
 extern "C" {
 #endif
 
-/* Include size of POWER5+ L3 cache lines: 256 bytes */
+/*
+ * Most powerpc machines have 128 bytes cache lines, but to make sure
+ * there is no false sharing on all known Power hardware, use the
+ * largest known cache line size, which is the physical size of POWER5
+ * L3 cache lines (256 bytes).
+ *
+ * "Each slice [of the L3] is 12-way set-associative, with 4,096
+ * congruence classes of 256-byte lines managed as two 128-byte sectors
+ * to match the L2 line size."
+ *
+ * From: "POWER5 system microarchitecture",
+ *       IBM Journal of Research & Development,
+ *       vol. 49, no. 4/5, July/September 2005
+ *       https://www.eecg.utoronto.ca/~moshovos/ACA08/readings/power5.pdf
+ *
+ * This value is a compile-time constant, which prevents us from
+ * querying the processor for the cache line size at runtime. We
+ * therefore need to be pessimistic and assume the largest known cache
+ * line size.
+ *
+ * This value is exposed through public headers, so tuning it for
+ * specific environments is a concern for ABI compatibility between
+ * applications and liburcu.
+ */
 #define CAA_CACHE_LINE_SIZE	256
 
 #ifdef __NO_LWSYNC__
@@ -63,7 +74,7 @@ extern "C" {
 	__extension__					\
 	({ 						\
 		unsigned long rval;			\
-		__asm__ __volatile__ ("mftbl %0" : "=r" (rval));	\
+		__asm__ __volatile__ ("mftb %0" : "=r" (rval));	\
 		rval;					\
 	})