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copied!<p>Without stating the application it is difficult to just guess what is causing the slow running of the application. If you want to go for a detailed analysis, we can consider following factors - </p> <ul> <li><p><strong>InterProcessor Communication</strong> : How much the threads in your application communicate with each other. If they communicate very often, then you will have overhead due to this behavior</p></li> <li><p><strong>Processor Cache Architecture</strong> : This is another important factor to see. You should know how the caches of the processor are going to be affected due to threads running on different processor. How much thrashing is going to happen at shared caches.</p></li> <li><p><strong>Page Faults</strong> : Maybe running on single processor is causing less number of page faults due to sequential nature of your program?</p></li> <li><p><strong>Locks</strong> : Lock overheads in your code? This should not cause a slowdown. But in addition to the above mentioned factors, this might add up to some overhead.</p></li> <li><p><strong>NoC on the processor</strong> : Definitely, if you allocate different threads to different processor cores, and they are communicating, then you need to know what is the path they are taking. Is there a dedicated connection between them? Perhaps you should have a look at this <a href="http://terboven.wordpress.com/2010/10/18/examining-the-numa-architecture-of-a-8-socket-nehalem-ex/" rel="nofollow">link</a>.</p></li> <li><p><strong>Processor Load</strong> : Last but not the least is that, I hope you are not having other tasks running on other processor cores, causing a lot of context-switches. Context switch is typically very expensive.</p></li> <li><p><strong>Temperature</strong> : One effect you should consider is of the processor clock being slowed down if the cpu core is heating up. I think, you will not have this effect, but it also largely depends on the ambient temperature.</p></li> </ul>

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