Dual core affinity control

[NapalmDeath]

Using an AMD Opteron Dual core 175 cpu, and the AMD/MS affinity patch, you can move processes/games to either core using taskmaster.

Would there be a benefit shifting a game to core 2 which seems to sit mostly idle, with the assumption XP and other programs would be consuming cycles on core 1?

Most folks seem to say leave all process affinity set to core 1 + core 2.
Does this assume some program is load balancing across the cores?

 

[Scali2]

By default the OS will balance the tasks over all the cores.
Limiting affinity to only one CPU or core is mainly done to improve cache coherency and avoid memory sharing issues, which can be especially troublesome on NUMA-machines.
In general, just having the OS balance everything over all cores is the best situation.

 

[visaris]

Most folks seem to say leave all process affinity set to core 1 + core 2. Does this assume some program is load balancing across the cores?

The operating system, Windows XP in this case, will move a process between cores whenever it thinks doing so is the right thing to do from a performance standpoint. In most cases, the OS will make the right choice, and you will not need to change anything.

I would only mess with the affinity if you are having issues or are simply curious. In short, the affinity will "lock" a process so that said process can only run on some subset of the availble cores.

Not sure what you mean by "load balancing". A single thread can only run on one core at a time. The only way one could say a single thread is being "load balanced" is if the thread is being moved between cores to make better use of free cycles. Still, I wouldn't describe things that way, and I wouldn't say "across the cores" as you do. I would rather say something like "moved around from core to core".

 

[NapalmDeath]

Thanks that makes sense.

Still when I play a game, one core is 100%, while the other is 0-8% utilized.
Hence the question.

 

[Scali2]

That's because games generally only have one thread which does all the processing.
There may be additional threads, but they're generally for special tasks like network and audio, and don't actually do much rather than wait for their turn to send or retrieve some data.
Apparently the OS chooses to keep that one thread on the same core at all times, because that gives the best performance (or perhaps the game requests it itself, any application and any thread can set its own affinity).