Channels ▼

Christopher Diggins

Dr. Dobb's Bloggers

Bit by the Cache

February 12, 2010

While profiling the parallel list operators for Heron I kept running into some really unsettling results. Only getting 25-40% increase in speed for even the most trivially parallelizable computations, on my dual-core machine. The most likely culprit: the cache.

Optimizing multi-threaded code can be a bit tricky if you aren't a low-level assembler junky. After profiling the heck out of my applications and doing tons of experiments, I just couldn't squeeze the maximum theoretical performance out of my dual-core machine for the most trivial cases. 

It turns out that I am doing a really bad job of managing my cache. For example I had a 32 megabyte array which I was processing simultaneously in two chunks. One core would work on the beginning, and the other core in the middle.  

Related Reading


More Insights






Currently we allow the following HTML tags in comments:

Single tags

These tags can be used alone and don't need an ending tag.

<br> Defines a single line break

<hr> Defines a horizontal line

Matching tags

These require an ending tag - e.g. <i>italic text</i>

<a> Defines an anchor

<b> Defines bold text

<big> Defines big text

<blockquote> Defines a long quotation

<caption> Defines a table caption

<cite> Defines a citation

<code> Defines computer code text

<em> Defines emphasized text

<fieldset> Defines a border around elements in a form

<h1> This is heading 1

<h2> This is heading 2

<h3> This is heading 3

<h4> This is heading 4

<h5> This is heading 5

<h6> This is heading 6

<i> Defines italic text

<p> Defines a paragraph

<pre> Defines preformatted text

<q> Defines a short quotation

<samp> Defines sample computer code text

<small> Defines small text

<span> Defines a section in a document

<s> Defines strikethrough text

<strike> Defines strikethrough text

<strong> Defines strong text

<sub> Defines subscripted text

<sup> Defines superscripted text

<u> Defines underlined text

Dr. Dobb's encourages readers to engage in spirited, healthy debate, including taking us to task. However, Dr. Dobb's moderates all comments posted to our site, and reserves the right to modify or remove any content that it determines to be derogatory, offensive, inflammatory, vulgar, irrelevant/off-topic, racist or obvious marketing or spam. Dr. Dobb's further reserves the right to disable the profile of any commenter participating in said activities.

 
Disqus Tips To upload an avatar photo, first complete your Disqus profile. | View the list of supported HTML tags you can use to style comments. | Please read our commenting policy.
 


Video