SMP question...

[Jon]

I recently got the 2nd 1GHz P3 for my VP6 and am very disappointed in my WU production with it.

With one processor overclocked to 1.125GHz (150MHz FSB) I was averaging right around 6hr WU times. Since putting in the 2nd one (same stepping cD0) I have not been able to overclock it so it is running at the stock 1GHz which really doesn't bother me much but the times to finish a WU has risen to over 8hrs. I've gone from an average of about 170MegaFLOPs an hour to barely over 120...this is per processor.

I can't really see losing 17MHz on my bus and 125MHz on the processor as causing this kind've differential in processing times. Sure, some of it probably has to do with sharing time on the bus as well as bandwidth, but losing over 2hrs? Doesn't seem right to me.

Just wondering what those of you with dual crunchers have to say about it. Is that just the way it works?

Overall production has increased but not nearly as much as I had hoped.

[JigPu]

Well, since I've never crunched on anything with more than one CPU, I can't help you much. However, there is something that might cause it (I think...). Have you set the processor affinity for the CLC? If not, that might be it. Both programs are using both CPUs, and each slows the other down. However, there is a way to set the CLC to run on a specific CPU, and that may help you out. Just set one client to run on one CPU and the other client to run on the other. Dunno the command off the top of my head though.... Mabey someone else?

JigPu

[Jon]

Affinity is set correctly in SETI Driver. One instance for each CPU so that's not it...

May just have to live with it.

[Mictlan]

PIII dual setup has a small problem: The two CPU share the memory bandwidth.....Athlon MP have independent memory channels.

Even with this small caveat, dual PIII setups kick the butt of Athlon MP setups.....maybe with DDR you won't be seeing that small problem (more of this later when I manage to get my dual PIII DDR setup) :)

[TC]

Having two cpu's adds some extra overhead for the OS, plus the memory sharing already mentioned.

[Jon]

That's what I figured.

Oh well, least I'll know what to expect when the 1Ghz comes in for my other dually.

Seems like such a waste though.

[TC]

Originally posted by Jon
That's what I figured.

Oh well, least I'll know what to expect when the 1Ghz comes in for my other dually.

Seems like such a waste though.

Well keep in mind when you have a dual machine you need to have at least times as much ram as you would for a similar single system - that's minimum. I wouldn't take less than 512-640K on a dual system because to reall tweak it you need to enable large file cache and other such tweaks that need lots of ram - and this makes a big difference on dually boxes.