SMP performance murdered when running single threaded app?

[VoraciousGorak]

So while I or my wife plays World of Warcraft, SMP performance drops by 75-90%. World of Warcraft, when nothing else is running, uses maybe 20-30% of my CPU power, but it does like to fully eat one core. Despite the fact that F@H continues to use the rest of my CPU time, it seems it's being throttled by one core being used.

Is there any way around this? I'd think that if it was limited by the core that WoW uses, then the CPU usage on the other cores would drop too, or the performance hit would be so bad.

 

[riotcity76]

I'm not quite sure on this, but I think I've heard this happening before. Try running the flag -smp 3 (assuming you have 4 threads) and use Task Manager to keep wow using the remaining unused core (set affinity).

 

[kup]

There is an app you can use to permanently bind executables to particular cores, I'll find it for you.

 

[VoraciousGorak]

Would it be better to run four individual F@H clients, or one SMP and one single-threaded client for situations like mine?

 

[kup]

SMP on 3 cores would still yield a better result than the single core clients, IMO.

 

[riotcity76]

What kup said. Although... I have heard that some WUs run worse on an odd number of cores. Overall though smp 3 is probably the best alternative.

 

[yuri04]

yup, all of the above is true..

the SMP client scales pretty horribly when the CPU is actually used. So it would indeed be a good solution (if you are running whatever it is you run for longer periods of time) to put an -smp 3 flag in place.

it will indeed yield better points then 3 or 4 uniprocessor clients, although the lines are fading.

it is also true that odd numbers of cores can produces problems due to I believe allocation of the cores.. This however will usually only happen with smp 7 and higher. so you should be safe with 3. Do note that with the new v7 client it is impossible to select an odd number of cores.