I have the same experience as Erik. My quad core CPU gets about 40% to 50% more output from 8 threads as from 4.
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Erik van der Werf Sent: Monday, May 12, 2014 11:39 AM To: [email protected] Subject: Re: [Computer-go] C++11; threads This is not accurate. In my experience you should expect a substantial performance increase from hyperthreading. (For my program on an i7-3930 it was something like a 40%, Zen got a similar number, others on this list have claimed even higher numbers, e.g., see: http://dvandva.org/pipermail/computer-go/2012-August/005298.html). Erik On Mon, May 12, 2014 at 5:06 PM, Mikko Aarnos <[email protected]> wrote: > CPU cores are meant to be used by a single thread only. You can use > more, but this rests on the assumption that two(or more) threads can > effectively utilize a single core without too much competition over > resources. This assumption is true in most situations, e.g. when we > have to wait for IO or server queries or things like that often, and > in these cases using HT can give a small performance boost. Now, here > we are only utilizing the CPU. In this case the threads are only > getting into each other's way. The effects of this can be seen very > clearly with your program. It seems to scale perfectly, or very nearly > so, as long as you don't use more threads than you have actual cores > on your computer. When you go above that limit the scaling goes to > hell and you get no improvement at all. The only way to solve your > scaling problem is to get rid of the competing threads by turning off HT. I did this and have never looked back. > > -Mikko Aarnos > > _______________________________________________ > Computer-go mailing list > [email protected] > http://dvandva.org/cgi-bin/mailman/listinfo/computer-go _______________________________________________ Computer-go mailing list [email protected] http://dvandva.org/cgi-bin/mailman/listinfo/computer-go _______________________________________________ Computer-go mailing list [email protected] http://dvandva.org/cgi-bin/mailman/listinfo/computer-go
