Hyper Threading On or Off ??

[Sean Evans]

Hello group,

If I have a Quad Core 720QM for computer chess is it better to leave HT off or HT on. In addition, how do I turn HT off and on. I will be using Windows 7.

Thank you,

Sean

[hyatt]

Hello group,

If I have a Quad Core 720QM for computer chess is it better to leave HT off or HT on. In addition, how do I turn HT off and on. I will be using Windows 7.

Thank you,

Sean

It is OK to leave it on, if the operating system is smart. For example, if you have a quad-core chip, with hyper-threading on it will look like 8 cores to the operating system. You would never want to run 8 threads with a chess program, but if you run just four, Linux (for example, as I do not know about windows) will schedule each thread on a different physical core. It would be terrible if it scheduled the 4 threads on two cores since it would still see 4 processors being used, but each two logical processors share everything and do not execute parallel things very efficiently compared to separate real processors.

If you are not sure, I'd turn it off. And I would always turn "turbo-boost" off. It's a crock that screws up all sorts of benchmark timing information.

[Uly]

Specifically for Rybka, it hurts, unless you set up affinities manually.

[hyatt]

Specifically for Rybka, it hurts, unless you set up affinities manually.

Just need a good operating system. Linux will handle this perfectly, and automatically. When we got our first i7-based box to test, I beat on this a lot and Ingo's process scheduler does exactly what it is supposed to do. Old versions were not so good and I kept SMT disabled in my old PIV xeon, but with kernels from the last year or so, this works flawlessly.