Thursday, August 18, 2016

Intel PGO Optimizations Lead to 20% Faster WordPress on AWS

Profile-guided Optimization (PGO) is a technique that improves the performance of applications. It requires profiling data, which is later passed to the compiler and can be obtained after a test run of the application. The profiling data contains information about code areas that are most frequently used, and by knowing these areas, the compiler is able to be more selective and specific in optimizing the application.

Bitnami has been working with Intel on adding Profile-guided Optimizations to selected Bitnami stacks and we started with a Bitnami WordPress stack. In summary, we saw the following:
  • Applying Profile-guided Optimizations to the Bitnami WordPress stack resulted in a 20% improvement in the page-load speed.
  • Additionally, applying some tweaks to the MariaDB configuration, we were able to decrease the page-load time a total of 34%, including the PGO change.
The machine used to get the results of these tests consisted of an AWS m3.medium instance with HVM and SSD, using a Ubuntu 14.04 image.

In order to test the improvements in page-load time, we are making use of the "php-cgi" executable which is included in the Bitnami WordPress stack. A sample command for testing a WordPress stack located at "/opt/bitnami" would be the following:

sudo /opt/bitnami/php/bin/php-cgi -c /opt/bitnami/php/etc/php.ini -T10,1000 /opt/bitnami/apps/wordpress/htdocs/index.php >/dev/null


The test will launch a total of 1000 requests, 10 at-a-time, and measure the time it takes until the last request finishes. With this result, we will be able to measure how quick our WordPress installation reacts.

Executing the command above in an original Bitnami WordPress stack, the results will look something like this:

$ sudo /opt/wordpress-4.5.3-2/php/bin/php-cgi -c /opt/wordpress-4.5.3-2/php/etc/php.ini -T10,1000 /opt/wordpress-4.5.3-2/apps/wordpress/htdocs/index.php >/dev/null

Elapsed time: 30.819571 sec


An important difference for the stack built with PGO-optimizations is that it bundles MariaDB (not MySQL), and that we added a few tweaks to the database configuration. These changes consist of a few added lines to the "mysqld" section in the database's "my.cnf" configuration file:

[mysqld]
query_cache_limit=1M
query_cache_size=16M
query_cache_type=1
thread_stack=192K
thread_cache_size=16
skip-external-locking=1
key_buffer_size=384M
sort_buffer_size=2M
read_buffer_size=2M
read_rnd_buffer_size=8M
myisam_sort_buffer_size=64M


These changes can be applied to the original WordPress installation too, resulting in an improvement in page-load speed up to 17,5% (comparing to the result of the first test):

$ sudo /opt/wordpress-4.5.3-2/php/bin/php-cgi -c /opt/wordpress-4.5.3-2/php/etc/php.ini -T10,1000 /opt/wordpress-4.5.3-2/apps/wordpress/htdocs/index.php >/dev/null

Elapsed time: 25.431113 sec


Now, combining the PGO-optimizations with the database tweaks mentioned above, it is possible to get up to 34% improvement in page-load time compared to the original Bitnami stack, and up to 20% if we compare it with the tweaked-database installation:

$ sudo /opt/wordpress-4.5.3-2/php/bin/php-cgi -c /opt/wordpress-4.5.3-2/php/etc/php.ini -T10,1000 /opt/wordpress-4.5.3-2/apps/wordpress/htdocs/index.php >/dev/null

Elapsed time: 20.310336 sec


As you can see, we get a 20.1% improvement in the page-load speed that are PGO-only related.
If we compare it with the original and non-modified WordPress stack (which does not include any database tweaks), the page-load time is reduced up to 34.1%:



Are you interested in trying the PGO-optimized Bitnami WordPress stack? You can download it below:



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