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Re: [PATCH] benchtests: Add pthread_once common-case test.
- From: Siddhesh Poyarekar <siddhesh at redhat dot com>
- To: Torvald Riegel <triegel at redhat dot com>
- Cc: GLIBC Devel <libc-alpha at sourceware dot org>
- Date: Wed, 9 Oct 2013 07:34:06 +0530
- Subject: Re: [PATCH] benchtests: Add pthread_once common-case test.
- Authentication-results: sourceware.org; auth=none
- References: <1381266586 dot 18547 dot 1130 dot camel at triegel dot csb>
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