Author: Vincent Diepeveen
Date: 12:33:07 11/08/05
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On November 08, 2005 at 15:26:45, Vincent Diepeveen wrote: A small technical note. The multiprocessing idea that intel is introducing (on paper at least) for dual core cpu's such as the coming generation of dual core Xeons and Yonah, looks everything but impressive. It basically means that an access to the L2 will be slower and that it can't write simultaneously with 2 cpu's to L2, nor can it read to L2 when other core is writing. In short i have not much faith in the scaling of the intel dual cores at this moment. The L2 cache for computerchess is very important, because the L1 cache, which gets majority of the hits, still is too tiny for computerchess (at least for Diep). It's just 64KB in combined size for pentium-m. Especially when we move to 64 bits and code sizes increase because of that, that's too tiny from my viewpoint. Also for databases this will be a severe penalty. Further i didn't read much on how they plan to manage the instruction cache in the L2 cache. This is pretty relevant as it's one of the many reasons why opteron is so fast. >On November 08, 2005 at 13:17:42, Yar wrote: > >>Hello, >> >>Here is review (total 14 pages) of upcoming Intel's Xeon 5000 (Dempsey). Sorry >>its only in german. It seems its faster then Opeteron 280. >>http://www.tecchannel.de/server/hardware/432957/ >> >>With best regards, >> >>Yar > >It should be a fast cpu that Dempsey. However that Xeon will be there januari >2007 or so and it will have a price of i guess around 5000 euro a cpu in the >quad version, if you can get it for that, as you'll have to buy probably >1000 at a time to get them for around 4500 dollar a piece. > >So effectively a quad xeon dual core will be januari 2007 around $40k. > >By that time of course a quad opteron quad core is nearly 2 times faster >and exactly 2 times cheaper. > >Please note that it's not sure whether the IPC from the intel pentium-m at such >high clockspeeds and dual core will be better than from AMD. I'm counting at it >that it will be a lot slower, because in order to clock pentium-m higher, intel >will need to make the pipeline longer and will probably move from a 2 cycle L1 >to a 3 cycle L1. In which case the processor is similar to the opteron from >chessprogramming viewpoint. > >Of course the Xeons have bigger L2 or even L3 caches on chip than AMD. That's >nice for certain applications that are in benchmarks, but in reallife it's not a >huge advantage. > >A few MB's is plenty for computerchess at the moment. > >On the other hand, could you tell me whether this Xeon has an on die memory >controller or doesn't it have one? > >Because *that* matters a lot. Hashtables is a matter of TLB trashing memory >latencies to a big hashtable. With 64 bits cpu's and the clock that keeps >ticking, the RAM sizes will increase too, meaning that the latencies you lose to >TLB trashing (transpositiontable , eval table, not so much pawntable as that'll >be in L2 cache for majority of accesses) are significant. > >If intel plans to do that via some sort of chipset off chip, then that is a huge >drawback of this Xeon cpu for databases and chess. At database benchmarks, using >some small database they can get away with a big L2/L3 then, but in real life >there is no escape there. It's just dead slow. > >So i do look forward to pentium-m, but the price at which intel usually sells >good cpu's doesn't mean that we will see more quads online. > >Vincent
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