Workers, Threads, Helper Threads, Cores, Affinity.

[lorgix]

Hello,


This is a jungle.

I'm confused to say the least.

I'm now running prime95 in 64bit Windows 7 on an i3 540.

That means two cores, with two logical processors on each.

Could someone explain what settings I should use?

How many workers? How many threads? Well the title says most of it...


I've done some experimenting, but I'm not satisfied.

[petrw1]

Originally Posted by lorgix

Hello,


This is a jungle.

I'm confused to say the least.

I'm now running prime95 in 64bit Windows 7 on an i3 540.

That means two cores, with two logical processors on each.

Could someone explain what settings I should use?

How many workers? How many threads? Well the title says most of it...


I've done some experimenting, but I'm not satisfied.

There are others that can give you more complete answers but the most important point is to run no more workers than you have PHYSICAL cores.

You can experiment with 1 or 2 threads per worker. I have found that in some cases the helper "helps" a bit but in other cases it makes it slightly worse. Even on the same PC some work types might benefit from a helper and some might be worse.

[Commaster]

In my opinion, TF works fine with all LOGICAL cores running. (tested for a looong time on my i7) So, it depends on the worktype you're running. For TF that makes 4 workers, 1 thread each, and set affinity for each worker on his own core.

[lorgix]

Thanks for responding.

It's obviously complicated....

Would it be crazy to turn off HT? I mean I like to multi-task, but Windows doesn't appear to be doing a very good job of it...

[Commaster]

I tried turning HT off. So much more lags came up that I hated it and turned HT on asap. IMO, Windows 7 is mature enough to handle this much of multitasking.
HT is not bad. You just would better ignore it on heavy workunits and use it on some easy ones, like TF or very low ECM.

[lorgix]

I occasionally run an admittedly high number of computing sessions. That could include PFGW, Prime95, MultiSieve, YAFU..

And frankly I'm a little disappointed that I can't get them to get along.

Too many tasks and suddenly one of them may get like zero ( 0 ) CPU time.

Is there a trick to this? I've tried playing with priority & affinity.


I'm pretty tempted by AMD Phenom II X6 1055T... Not for this machine obv, but for an entirely new one. Just hope that thing doesn't feel the need to pretend to have more processors than it actually has cores....

[lavalamp]

Originally Posted by lorgix

I occasionally run an admittedly high number of computing sessions. That could include PFGW, Prime95, MultiSieve, YAFU..

And frankly I'm a little disappointed that I can't get them to get along.

Too many tasks and suddenly one of them may get like zero ( 0 ) CPU time.

Is there a trick to this? I've tried playing with priority & affinity.

Personally I just set the CPU affinity and things run fine. Be aware though that if a program closes, and then runs again later, you'll need to set the affinity again. You can get programs to automatically do this for you, I have one called Core Affinity Resident, works on XP, Vista and 7, and it's free. Of course, if you run 5 programs when you only have 4 logical cores, you can't expect them not to fight.

I don't like leaving it up to Windows to decide what cores things run on, it has a tenancy to bound threads around cores for no apparent reason and that means programs don't get to take full advantage of the L1 and L2 caches, constantly having to wait for the slower L3 cache. For most things this doesn't matter, I don't care if Firefox could be 5% faster, but I do care if ECM could be 5% faster if I plan on running curves that will take a week.

Note that I haven't actually measured the performance benefit (if any) for setting CPU affinity vs. leaving it up to windows, but since I have the process all automated and therefore takes zero time for me to do, I don't plan on measuring it either.

Hyperthreading is very handy, I have 4 physical cores, but 8 logical cores, that means I can run 8 threads. I can choose to run things on all 8 threads, and I get a nice bonus for some of them. For example when sieving or trial factoring I get a 25% boost in overall throughput by using 8 threads. It's like having a 5 core CPU! However, the cost is that the PC becomes sluggish and less responsive. If however I decide to run just 4 threads, the PC is still very productive, and I can actually use it to do things, and even play games.

[mdettweiler]

Originally Posted by lorgix

I'm pretty tempted by AMD Phenom II X6 1055T... Not for this machine obv, but for an entirely new one. Just hope that thing doesn't feel the need to pretend to have more processors than it actually has cores....

Not to worry, no AMDs have hyperthreading at this time. An X6 has six real cores, which appear to the OS as six processors. (Ditto for an X4, X3, X2, etc...)

[lorgix]

Originally Posted by mdettweiler

Not to worry, no AMDs have hyperthreading at this time. An X6 has six real cores, which appear to the OS as six processors. (Ditto for an X4, X3, X2, etc...)

And they are doing just fine without it as far as I can tell.

I'm also very much tempted by Phenom II X4 955 Black. A lot of operations for the money...

Could I possibly fit two of those (X4 955) on one motherboard?

[mdettweiler]

Originally Posted by lorgix

And they are doing just fine without it as far as I can tell.

I'm also very much tempted by Phenom II X4 955 Black. A lot of operations for the money...

Could I possibly fit two of those (X4 955) on one motherboard?

To put two CPUs on the same motherboard you usually need a server motherboard, which is generally very expensive. It would probably be cheaper to build two separate single-CPU machines.

AFAICT, the best "bang for the buck" in crunching CPUs right now are the Phenom II X6's. For just $30 more than the X4 955, you can get an X6 1055T (which, I believe, should be able to use most of the same motherboards as the X4), i.e. one and a half X4's in terms of crunching power.

[lorgix]

Originally Posted by mdettweiler

To put two CPUs on the same motherboard you usually need a server motherboard, which is generally very expensive. It would probably be cheaper to build two separate single-CPU machines.

AFAICT, the best "bang for the buck" in crunching CPUs right now are the Phenom II X6's. For just $30 more than the X4 955, you can get an X6 1055T (which, I believe, should be able to use most of the same motherboards as the X4), i.e. one and a half X4's in terms of crunching power.

I've heard that about X6 before, but I'm not sure it's true. At least where I live, yet.

I was hoping I could save on other equipment because I'm mostly interested in CPU cycles. But what you're saying is essentially that 2*X4 955 is too little for that reasoning to add up?

Are there any particular OS problems associated with using multiple CPUs?