Hi all,
this patch-let makes implements a GCC feature to hint the branch
prediction algorithms about the likely outcome of a test. This is useful
to optimize the case of singleton patterns (e.g.
CacheManager::GetInstance).
This implements the likely() and unlikely() macros.
Kinkie
# Bazaar merge directive format 2 (Bazaar 0.90)
# revision_id: [email protected]
# target_branch: file:///home/kinkie/squid/workspace/squid-trunk-co/
# testament_sha1: e69ce26d8ffa5a3519c81e25453faff4a0cb725b
# timestamp: 2010-10-12 17:42:32 +0200
# base_revision_id: [email protected]\
# xnwwkgwnuhy5oj0r
#
# Begin patch
=== added file 'include/branch-hints.h'
--- include/branch-hints.h 1970-01-01 00:00:00 +0000
+++ include/branch-hints.h 2010-10-12 15:42:26 +0000
@@ -0,0 +1,43 @@
+/*
+ * branch-hints.h (C) 2009 Francesco Chemolli <[email protected]>
+ *
+ * SQUID Web Proxy Cache http://www.squid-cache.org/
+ * ----------------------------------------------------------
+ *
+ * Squid is the result of efforts by numerous individuals from
+ * the Internet community; see the CONTRIBUTORS file for full
+ * details. Many organizations have provided support for Squid's
+ * development; see the SPONSORS file for full details. Squid is
+ * Copyrighted (C) 2001 by the Regents of the University of
+ * California; see the COPYRIGHT file for full details. Squid
+ * incorporates software developed and/or copyrighted by other
+ * sources; see the CREDITS file for full details.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA.
+ *
+ */
+
+#ifndef BRANCHHINTS_H_
+#define BRANCHHINTS_H_
+
+#if defined(__GNUC__)
+#define likely(x) __builtin_expect(!!(x), 1)
+#define unlikely(x) __builtin_expect(!!(x), 0)
+#else
+#define likely(x) (x)
+#define unlikely(x) (x)
+#endif /* __GNUC__ */
+
+#endif /* BRANCHHINTS_H_ */
=== modified file 'src/cache_manager.cc'
--- src/cache_manager.cc 2010-08-16 11:35:40 +0000
+++ src/cache_manager.cc 2010-10-12 15:42:26 +0000
@@ -33,6 +33,7 @@
*
*/
+#include "branch-hints.h"
#include "CacheManager.h"
#include "errorpage.h"
#include "HttpReply.h"
@@ -478,7 +479,7 @@
CacheManager*
CacheManager::GetInstance()
{
- if (instance == 0) {
+ if (unlikely(instance == 0)) {
debugs(16, 6, "CacheManager::GetInstance: starting cachemanager up");
instance = new CacheManager;
}
# Begin bundle
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