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benchtests: Add pthread_once common-case test.
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).
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Torvald Riegel committed Apr 10, 2014
1 parent a4c75cf commit 6a5d6ea
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6 changes: 6 additions & 0 deletions ChangeLog
@@ -1,3 +1,9 @@
2014-04-10 Torvald Riegel <triegel@redhat.com>

* benchtests/pthread_once-inputs: New file.
* benchtests/pthread_once-source.c: New file.
* benchtests/README: Update documentation.

2014-04-09 Igor Zamyatin <igor.zamyatin@intel.com>
H.J. Lu <hongjiu.lu@intel.com>

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3 changes: 2 additions & 1 deletion benchtests/Makefile
Expand Up @@ -23,7 +23,7 @@ subdir := benchtests

include ../Makeconfig
bench := acos acosh asin asinh atan atanh cos cosh exp exp2 ffs ffsll \
log log2 modf pow rint sin sincos sinh sqrt tan tanh
log log2 modf pow pthread_once rint sin sincos sinh sqrt tan tanh

# String function benchmarks.
string-bench := bcopy bzero memccpy memchr memcmp memcpy memmem memmove \
Expand Down Expand Up @@ -53,6 +53,7 @@ LDLIBS-bench-exp2 = -lm
LDLIBS-bench-log = -lm
LDLIBS-bench-log2 = -lm
LDLIBS-bench-pow = -lm
LDLIBS-bench-pthread_once = -lpthread
LDLIBS-bench-rint = -lm
LDLIBS-bench-sin = -lm
LDLIBS-bench-sinh = -lm
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2 changes: 2 additions & 0 deletions benchtests/README
Expand Up @@ -60,6 +60,8 @@ 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
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9 changes: 9 additions & 0 deletions benchtests/pthread_once-inputs
@@ -0,0 +1,9 @@
# 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.py doesn't handle function pointers, so we just use void *:
## args: pthread_once_t *:void *
## includes: pthread.h
## include-sources: pthread_once-source.c
&once, once_handler
25 changes: 25 additions & 0 deletions benchtests/pthread_once-source.c
@@ -0,0 +1,25 @@
/* Measure pthread_once best-case latency (i.e., when already initialized.
Copyright (C) 2014 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)
{
}

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