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multi-threading slower than single thread [message #24788]

Fri, 29 January 2010 22:23

nixnixnix
Messages: 415
Registered: February 2007
Location: Kelowna, British Columbia

Senior Member

Hi,

I have a very strange thing happening. Just over 1 year ago I wrote some multi-threading code that scaled the performance of my calculation linearly with number of virtual cores. However, now that same code performs worse than a single thread.

Using my SVN I have stepped back in time one year and recompiled that code and it performs as I remember it.

My code now is many many times slower and the single threaded version performs better than the multithreaded version.

This applies to several very different and separate calculations I do. It applies to the linux and windows builds, both 32 and 64 bit.

I checked out a version from about 7 months ago and it is slower than the 1 year old version but not nearly as slow as my latest version. The code that does the calculations is the same though. It appears to be something to do with the general properties (size?) of the exe that is causing it to perform hundreds of times worse.

Does anybody have any idea as to what might cause this type of slow down please? I am going out of my mind trying to hunt it down. Any ideas welcome.

Nick

EDIT: there is a difference in what the functions do, still hunting down how to fix it but please feel free to delete this thread as a red-herring Embarassed

[Updated on: Sat, 30 January 2010 01:23]

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