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Re: multi-threading slower than single thread [message #24792 is a reply to message #24788]

Sat, 30 January 2010 08:48

mirek
Messages: 14291
Registered: November 2005

Ultimate Member

nixnixnix wrote on Fri, 29 January 2010 16:23

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.

Generally, this is a sign that either synchronization costs or thread management costs are higher than gains of using multiple cores....

Hard to comment more withou seeing the code.

When you are speaking about svn, are you speaking about U++ (then it would be useful to at least provide svn revision which appears to break it) or your code?

Quote:

(size?) of the exe that is causing it to perform hundreds of times worse.

Not really impossible. Can be a cache issue. But IMO unlikely.

Mirek

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[Message index]

		multi-threading slower than single thread By: nixnixnix on Fri, 29 January 2010 22:23
		Re: multi-threading slower than single thread By: mirek on Sat, 30 January 2010 08:48
		Re: multi-threading slower than single thread By: Didier on Sat, 30 January 2010 10:35
		Re: multi-threading slower than single thread By: nixnixnix on Mon, 01 February 2010 07:29
		Re: multi-threading slower than single thread By: mirek on Mon, 01 February 2010 12:58
		Re: multi-threading slower than single thread By: nixnixnix on Mon, 08 February 2010 21:47
		Re: multi-threading slower than single thread By: mirek on Mon, 08 February 2010 23:54
		Re: multi-threading slower than single thread By: nixnixnix on Tue, 09 February 2010 01:34
		Re: multi-threading slower than single thread By: mirek on Mon, 15 February 2010 12:44
		Re: multi-threading slower than single thread By: nixnixnix on Mon, 01 March 2010 21:25

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