[PATCH] benchtests: Add pthread_once common-case test.

[Torvald Riegel <triegel at redhat dot com>]

This adds a benchtest for the common-case scenario for pthread_once.

We have a single thread that runs a no-op initialization once and then
repeatedly runs checks of the initialization (i.e., an acquire load and
conditional jump) in a tight loop.  This gives us, on average, the
best-case latency of pthread_once (the initialization is the
exactly-once slow path, and we're not looking at initialization-related
synchronization overheads in this case).  I'm adding this to investigate
whether we still need the x86-custom pthread_once version written in
assembler, or whether we can use the generic version without a
performance loss (both use the same algorithm).

This needs the other patch that adds the include-sources directive to
scripts/bench.pl.

OK?

commit a26cb3d5ffd621b756a951a53bd160811d0f3fae
Author: Torvald Riegel <triegel@redhat.com>
Date:   Tue Oct 8 14:17:01 2013 +0300

    benchtests: Add pthread_once common-case test.
    
    	* benchtests/pthread_once-inputs: New file.
    	* benchtests/pthread_once-source.c: New file.
    	* benchtests/README: Update documentation.

diff --git a/ChangeLog b/ChangeLog
index 1acd57c..61da75c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 2013-10-08  Torvald Riegel  <triegel@redhat.com>
 
+	* benchtests/pthread_once-inputs: New file.
+	* benchtests/pthread_once-source.c: New file.
+	* benchtests/README: Update documentation.
+
+2013-10-08  Torvald Riegel  <triegel@redhat.com>
+
 	* scripts/bench.pl: Add include-sources directive.
 	* benchtests/README: Update documentation.
 
diff --git a/benchtests/Makefile b/benchtests/Makefile
index aec395a..2eb1393 100644
--- a/benchtests/Makefile
+++ b/benchtests/Makefile
@@ -20,8 +20,8 @@
 # Add benchmark functions in alphabetical order.
 
 subdir := benchtests
-bench := acos acosh asin asinh atan atanh cos cosh exp log modf pow rint sin \
-	 sincos sinh tan tanh
+bench := acos acosh asin asinh atan atanh cos cosh exp log modf pow \
+	 pthread_once rint sin sincos sinh tan tanh
 
 # String function benchmarks.
 string-bench := bcopy bzero memccpy memchr memcmp memcpy memmem memmove \
@@ -45,6 +45,7 @@ LDLIBS-bench-cosh = -lm
 LDLIBS-bench-exp = -lm
 LDLIBS-bench-log = -lm
 LDLIBS-bench-pow = -lm
+LDLIBS-bench-pthread_once = -lpthread
 LDLIBS-bench-rint = -lm
 LDLIBS-bench-sin = -lm
 LDLIBS-bench-sinh = -lm
diff --git a/benchtests/README b/benchtests/README
index 0c643a6..9dcbc53 100644
--- a/benchtests/README
+++ b/benchtests/README
@@ -57,6 +57,8 @@ one to add `foo' to the bench tests:
   - include-sources: This should be assigned a comma-separated list of source
     files that need to be included to provide definitions of global variables
     and functions (specifically, this includes using "#include "source").
+    See pthread_once-inputs and pthreads_once-source.c for an example of how
+    to use this to benchmark a function that needs state across several calls.
   - name: See following section for instructions on how to use this directive.
 
   Lines beginning with a single hash '#' are treated as comments.  See
diff --git a/benchtests/pthread_once-inputs b/benchtests/pthread_once-inputs
new file mode 100644
index 0000000..040bc5c
--- /dev/null
+++ b/benchtests/pthread_once-inputs
@@ -0,0 +1,10 @@
+# This tests the common-case scenario for pthread_once.
+# We have a single thread that runs a no-op initialization once and then
+# repeatedly runs checks of the initialization (i.e., an acquire load and
+# conditional jump) in a tight loop. 
+# scripts/bench.pl doesn't handle function pointers, so we just use void *:
+## args: pthread_once_t *:void *
+## ret: void
+## includes: pthread.h
+## include-sources: pthread_once-source.c
+&once, once_handler
diff --git a/benchtests/pthread_once-source.c b/benchtests/pthread_once-source.c
new file mode 100644
index 0000000..04e70d6
--- /dev/null
+++ b/benchtests/pthread_once-source.c
@@ -0,0 +1,23 @@
+/* Copyright (C) 2013 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C 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.
+
+   The GNU C 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 the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+static pthread_once_t once = PTHREAD_ONCE_INIT;
+
+static void
+once_handler (void)
+{
+}