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


On Wed, Oct 09, 2013 at 12:09:46AM +0300, Torvald Riegel wrote:
> 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.
>  

You don't need to post ChangeLog diffs here.  Also, if you have back
to back changes on the same day, you could merge the entries by
leaving a blank line between the change sets like this:

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.

	* 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)
> +{
> +}

I am OK with this patch, but please wait for another review before you
check this in.

Siddhesh


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