mirror of
https://github.com/clearlinux/clear-linux-documentation.git
synced 2026-06-30 01:35:59 +00:00
Kevin Putnam
277 lines
7.9 KiB
ReStructuredText
277 lines
7.9 KiB
ReStructuredText
.. _fmv:
|
|
|
|
Use the function multi-version patch generator
|
|
##############################################
|
|
|
|
CPU architectures often gain interesting new instructions as they evolve but
|
|
application developers find it difficult to take advantage of those
|
|
instructions. The reluctance to lose backward-compatibility is one of the
|
|
main roadblocks slowing developers from using advancements in newer computing
|
|
architectures. :abbr:`FMV (Function Multi-Versioning)`, which first appeared
|
|
in `GCC`_ 4.8, is a way to have multiple implementations of a function, each
|
|
using a different architecture specialized instruction-set extensions. GCC
|
|
6 introduces changes to FMV to make it even easier to bring architecture-
|
|
based optimizations to the application code.
|
|
|
|
In this tutorial we will use FMV on general code and on
|
|
:abbr:`FFT (Fast Fourier Transform)` library code. Upon completing the
|
|
tutorial, you will be able to use this technology on your code and use the
|
|
libraries to deploy architecture-based optimizations to your application code.
|
|
|
|
Install and configure a Clear Linux host on bare metal
|
|
******************************************************
|
|
|
|
First, follow our guide to :ref:`bare-metal-install`.
|
|
|
|
Once the bare metal installation and initial configuration are complete,
|
|
add the `desktop-dev` bundle to the system.
|
|
|
|
`desktop-dev`: contains the necessary development tools like GCC and Perl\*.
|
|
|
|
To install the bundles, run the following command in the :file:`$HOME`
|
|
directory:
|
|
|
|
.. code-block:: bash
|
|
|
|
sudo swupd bundle-add desktop-dev
|
|
|
|
Detect loop vectorization candidates
|
|
************************************
|
|
|
|
Now, we need to detect the loop vectorization candidates to be cloned for
|
|
multiple platforms with FMV. As an example, we will use the following
|
|
simple C code:
|
|
|
|
.. code-block:: c
|
|
:linenos:
|
|
|
|
#include <stdio.h>
|
|
#include <stdlib.h>
|
|
#include <sys/time.h>
|
|
#define MAX 1000000
|
|
|
|
int a[256], b[256], c[256];
|
|
|
|
void foo(){
|
|
int i,x;
|
|
for (x=0; x<MAX; x++){
|
|
for (i=0; i<256; i++){
|
|
a[i] = b[i] + c[i];
|
|
}
|
|
}
|
|
}
|
|
|
|
|
|
int main(){
|
|
foo();
|
|
return 0;
|
|
}
|
|
|
|
Save the example code as :file:`example.c` in the current directory and build
|
|
with the following flags:
|
|
|
|
.. code-block:: bash
|
|
|
|
gcc -O3 -fopt-info-vec example.c -o example
|
|
|
|
The build generates the following output:
|
|
|
|
.. code-block:: console
|
|
|
|
example.c:11:9: note: loop vectorized
|
|
example.c:11:9: note: loop vectorized
|
|
|
|
The output shows that line 11 is a good candidate for vectorization:
|
|
|
|
.. code-block:: c
|
|
|
|
for (i=0; i<256; i++){
|
|
a[i] = b[i] + c[i];
|
|
|
|
Generate the FMV patch
|
|
**********************
|
|
|
|
To generate the FMV patch with the `make-fmv-patch`_ project, we
|
|
must clone the project and generate a log file with the loop vectorized
|
|
information:
|
|
|
|
.. code-block:: bash
|
|
|
|
git clone https://github.com/clearlinux/make-fmv-patch.git
|
|
gcc -O3 -fopt-info-vec example.c -o example &> log
|
|
|
|
To generate the patch files, execute:
|
|
|
|
.. code-block:: bash
|
|
|
|
perl ./make-fmv-patch/make-fmv-patch.pl log .
|
|
|
|
The :file:`make-fmv-patch.pl` script takes two arguments: `<buildlog>` and
|
|
`<sourcecode>`. Replace `<buildlog>` and `<sourcecode>` with the proper
|
|
values and execute:
|
|
|
|
.. code-block:: bash
|
|
|
|
perl make-fmv-patch.pl <buildlog> <sourcecode>
|
|
|
|
The command generates the following :file:`example.c.patch` patch:
|
|
|
|
.. code-block:: console
|
|
|
|
--- ./example.c 2017-09-27 16:05:42.279505430 +0000
|
|
+++ ./example.c~ 2017-09-27 16:19:11.691544026 +0000
|
|
@@ -5,6 +5,7 @@
|
|
|
|
int a[256], b[256], c[256];
|
|
|
|
+__attribute__((target_clones("avx2","arch=atom","default")))
|
|
void foo(){
|
|
int i,x;
|
|
for (x=0; x<MAX; x++){
|
|
|
|
We recommend you use the :file:`make-fmv-patch` script to add the attribute
|
|
generating the target clones on the function `foo`. Thus, we can have the
|
|
following code:
|
|
|
|
.. code-block:: c
|
|
|
|
#include <stdio.h>
|
|
#include <stdlib.h>
|
|
#include <sys/time.h>
|
|
#define MAX 1000000
|
|
|
|
int a[256], b[256], c[256];
|
|
|
|
__attribute__((target_clones("avx2","arch=atom","default")))
|
|
void foo(){
|
|
int i,x;
|
|
for (x=0; x<MAX; x++){
|
|
for (i=0; i<256; i++){
|
|
a[i] = b[i] + c[i];
|
|
}
|
|
}
|
|
}
|
|
|
|
|
|
int main(){
|
|
foo();
|
|
return 0;
|
|
}
|
|
|
|
Changing the value of the `$avx2` variable, we can change the target
|
|
clones when adding the patches or in the :file:`make-fmv-patch.pl` script:
|
|
|
|
.. code-block:: perl
|
|
|
|
my $avx2 = '__attribute__((target_clones("avx2","arch=atom","default")))'."\n";
|
|
|
|
Compile the code again with FMV and add the option to analyze the `objdump`
|
|
log:
|
|
|
|
.. code-block:: bash
|
|
|
|
gcc -O3 example.c -o example -g
|
|
objdump -S example | less
|
|
|
|
You can see the multiple clones of the `foo` function:
|
|
|
|
.. code-block:: console
|
|
|
|
foo
|
|
foo.avx2.0
|
|
foo.arch_atom.1
|
|
|
|
The cloned functions use AVX2 registers and vectorized instructions. To
|
|
verify, enter the following commands:
|
|
|
|
::
|
|
|
|
vpaddd (%r8,%rax,1),%ymm0,%ymm0
|
|
vmovdqu %ymm0,(%rcx,%rax,1)
|
|
|
|
FTT project example
|
|
*******************
|
|
|
|
To follow the same approach with a package like FFT, we must use the
|
|
`-fopt-info-vec` flag to get a build log file similar to:
|
|
|
|
.. code-block:: bash
|
|
|
|
~/make-fmv-patch/make-fmv-patch.pl results/build.log fftw-3.3.6-pl2/
|
|
|
|
patching fftw-3.3.6-pl2/libbench2/verify-lib.c @ lines (36 114 151 162 173 195 215 284)
|
|
patching fftw-3.3.6-pl2/tools/fftw-wisdom.c @ lines (150)
|
|
patching fftw-3.3.6-pl2/libbench2/speed.c @ lines (26)
|
|
patching fftw-3.3.6-pl2/tests/bench.c @ lines (27)
|
|
patching fftw-3.3.6-pl2/libbench2/util.c @ lines (181)
|
|
patching fftw-3.3.6-pl2/libbench2/problem.c @ lines (229)
|
|
patching fftw-3.3.6-pl2/tests/fftw-bench.c @ lines (101 147 162 249)
|
|
patching fftw-3.3.6-pl2/libbench2/mp.c @ lines (79 190 215)
|
|
patching fftw-3.3.6-pl2/libbench2/caset.c @ lines (5)
|
|
patching fftw-3.3.6-pl2/libbench2/verify-r2r.c @ lines (44 187 197 207 316 333 723)
|
|
|
|
For example, the :file:`fftw-3.3.6-pl2/tools/fftw-wisdom.c.patch` file
|
|
generates the following patches:
|
|
|
|
.. code-block:: diff
|
|
:linenos:
|
|
|
|
--- fftw-3.3.6-pl2/libbench2/verify-lib.c 2017-01-27 21:08:13.000000000 +0000
|
|
+++ fftw-3.3.6-pl2/libbench2/verify-lib.c~ 2017-09-27 17:49:21.913802006 +0000
|
|
@@ -33,6 +33,7 @@
|
|
|
|
double dmax(double x, double y) { return (x > y) ? x : y; }
|
|
|
|
+__attribute__((target_clones("avx2","arch=atom","default")))
|
|
static double aerror(C *a, C *b, int n)
|
|
{
|
|
if (n > 0) {
|
|
@@ -111,6 +112,7 @@
|
|
}
|
|
|
|
/* make array hermitian */
|
|
+__attribute__((target_clones("avx2","arch=atom","default")))
|
|
void mkhermitian(C *A, int rank, const bench_iodim *dim, int stride)
|
|
{
|
|
if (rank == 0)
|
|
@@ -148,6 +150,7 @@
|
|
}
|
|
|
|
/* C = A + B */
|
|
+__attribute__((target_clones("avx2","arch=atom","default")))
|
|
void aadd(C *c, C *a, C *b, int n)
|
|
{
|
|
int i;
|
|
@@ -159,6 +162,7 @@
|
|
}
|
|
|
|
/* C = A - B */
|
|
+__attribute__((target_clones("avx2","arch=atom","default")))
|
|
void asub(C *c, C *a, C *b, int n)
|
|
{
|
|
int i;
|
|
@@ -170,6 +174,7 @@
|
|
}
|
|
|
|
/* B = rotate left A (complex) */
|
|
+__attribute__((target_clones("avx2","arch=atom","default")))
|
|
void arol(C *b, C *a, int n, int nb, int na)
|
|
{
|
|
int i, ib, ia;
|
|
@@ -192,6 +197,7 @@
|
|
}
|
|
}
|
|
|
|
With these patches, we can select where to apply the FMV technology making
|
|
bringing architecture-based optimizations to application code even easier.
|
|
|
|
**Congratulations!**
|
|
|
|
You have successfully installed an FMV development environment on Clear
|
|
Linux. Furthermore, you used cutting edge compiler technology to improve the
|
|
performance of your application based on Intel Architecture technology and
|
|
profiling of the specific execution of your application.
|
|
|
|
.. _GCC: https://gcc.gnu.org
|
|
.. _make-fmv-patch: https://github.com/clearlinux/make-fmv-patch
|