Author: Robert Hyatt
Date: 07:55:28 08/04/05
Go up one level in this thread
On August 04, 2005 at 05:18:43, Vincent Diepeveen wrote: >On August 03, 2005 at 13:34:09, Robert Hyatt wrote: > >>On August 03, 2005 at 10:21:20, Gian-Carlo Pascutto wrote: >> >>>On August 03, 2005 at 10:13:45, Sedat wrote: >>> >>>>Hi there, >>>> >>>>Does anybody has any information about this processor ? >>>> >>>>-Can i run engine-matches with ponder on ? >>>> >>>>I mean: >>>>-Does the kns of the engines will fall down ? >>>> >>>>And if its possible to run ponder on matches : >>>>-is it enough just one processor or i need to buy two processors ? >>> >>>A single dualcore processor behaves almost exactly like a 2 processor machine. >>> >>>-- >>>GCP >> >>This needs a _lot_ more testing before saying that so positively. I've been >>testing on a quad dual-core box, and there are most definitely "issues" to deal >>with that I/we have not yet solved. There are some memory issues that I am >>working on quantifying, probably related to two cores sharing a memory bank and >>the associated bus contention. First cut on the quad 875 box produced some >>really ugly SMP results for me, with the NPS "scalability" only reaching 4X >>generally, where on the quad 850 I last tested on, it scaled perfectly for 1-4 >>processors... >> >>More as I work out the glitches (I hope).. > >This is because crafty doesn't scale. > >Not a hardware issue. Vincent, please go away and come back when you have some clue about what is being discussed. Crafty, using two cpus, on a quad single-core opteron, scales perfectly. Crafty, using two cpus, on a quad dual-core opteron, scales horribly. It isn't a "crafty issue". More when we find out exactly what it is... Crafty scales perfectly on dual opteron, quad opteron, and 8-way opterons. But the dual-core is adding a new problem that is currently undiscovered, but is probably an issue of two cores with one memory path that is shared. Or it is related to the MOESI cache coherency message bandwidth... > >Memory latency is 234 ns to get 8 bytes of TLB trashing memory from 250MB >buffers (in total 2GB ram for total testblock). Has zero to do with anything... > >Compare with 400 ns that your own dual Xeon needs to deliver the same >and compare with 700 ns that 8 processor Xeon needs. Has zero to do with anything... > >I guess the central lock structure in crafty breaks it at 8 cpu's. You are guessing wrong. It's already run on 8-way (and beyond) single-core boxes with zero problems... the dual-cores are experiencing problems at the moment... > >Diep is not central locking, of course tested to work at ugly latencies >until 500 cpu's and has zero problems with quad opteron dual core 1.8Ghz >at which i play at. > >Please note the latency for 2.2Ghz dual cores is far better because the >latency of each memory controller is somewhat dependant upon the speed of the >processor. Latency is no better/worse for dual-cores than single-cores. We are swapping them back and forth (same everything except for cpus) with zero problems and memory latency is not changing one iota... > >So the problem is not the hardware at all, but software issues within crafty. Nice to be able to debug something by reading tea-leaves. I'll report the _real_ problem(s) as it(they) are discovered... > >Any default x86-64 core 2.6.10 or later by default already is NUMA and works >perfectly. No need to compile your own core. Wrong answer. Default most recent redhat kernel crashes with numa=on. We just built a new kernel to fix this yesterday... still not scaling correctly on dual-cores, but scaling fine on single-cores... > >I installed Ubuntu at quad, upgraded to x86-64 kernel (thanks to Mridul >Muralidharan for his big help!) and it worked fine. > >Ubuntu is the superior distribution nowadays. > >Vincent
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