Author: Robert Hyatt
Date: 09:46:29 08/05/05
Go up one level in this thread
On August 05, 2005 at 08:36:14, Vincent Diepeveen wrote: >On August 04, 2005 at 10:55:28, Robert Hyatt wrote: > >>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". > >Oh yes it is a crafty issue. > >Just get Ubuntu and a default vanilla SMP kernel upgrade which takes just a few >seconds to upgrade and 1 reboot and run some decent software instead of crafty >and you'll see that software scales perfectly. So what? Different applications hit on different architectural features. There are plenty of applications that scale perfectly with hyper-threading also. But not _all_. > >> >>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... > >Aha so that Diep works perfectly on dual cores and scales perfectly on dual >cores (see www.sudhian.com) is because the dual cores are 'broken'? > >So not crafty is the problem but the dual core is the problem? I don't know what the "problem" is. I simply know that on a quad 850, crafty scales perfectly for 1-2-3-4 processors using NPS as the comparison factor. On the quad dual-core box it comes nowhere near that even using just two threads. What is causing it is a complete mystery at the moment. It could be hardware, software, bios, MB, memory, program bug, or anything. Hence I have only said "I don't know what the problem is other than it shows up on the dual cores but not on the single-cores..." > >Comeon. > >GROW UP! You need to but it appears that will never happen... > >Learn some decent SMP programming, instead of blaming the hardware. > >It works fine for everyone else. The latency just increased from 133ns to 234 ns >back to 200ns-220ns for 2.2Ghz dual cores. > >The real reason is how crafty has been SMP programmed. Multithreaded to mention >one thing, though that doesn't need to be a handicap as Nalimov indicated. > >With all kind of artificial tricks you can reprogram multithreaded programs to >multiprocessed programs :) but it isn't necessary. > >Of course you still lose that one register, but well that's the last of your >worries. The real problem is CRAFTY doesn't scale well at NUMA hardware above 2 >cpu's. At 4 cpu's you still hardly feel it, but at 8 cpu's you sure do. Then why do I not feel it at 4 on one box, but feel it at 2 on another? You keep dancing around _the_ issue here, as usual... your comments are simply off-the-wall, and not thought through. > >> >> >> >>> >>>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... > >Show us the output from a NUMA 8 way machine where you ran at. >8 processor Xeon, or that 8 way which you could get for world champs 2004 but >didn't get as 'crafty didn't run on it well' will do. There was no "8-way for the 2004 that crafty didn't run well on". No idea why you have to make things up when all else fails. I asked for and got access to a quad from AMD. Nothing more nothing less... They didn't have any 8-way boxes available or we would have been on one. > >> >>> >>>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 > >See results. Latency of single core at a dual is 111ns, versus 147ns for a >single cpu test at a dual core. > >>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... > >Software issues in crafty :) > >> >>> >>>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... > >You compare a 4 way crafty versus 8 way. > >I just told you, the problem is 8 way crafty at a NUMA machine. Will you _please_ stop and read. I am comparing 1-way crafty to 2-way crafty, and seeing a big problem. _not_ 8way. 8way definitely has a problem, but just running _two_ threads has a problem where it does not on the old 4-way box with 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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