Author: Charles Worthington
Date: 18:18:48 04/07/03
Go up one level in this thread
On April 02, 2003 at 22:07:39, Matthew White wrote: >On April 02, 2003 at 17:59:49, Pavel Blokhine wrote: > >>On April 02, 2003 at 13:30:16, Robert Hyatt wrote: >> >>>Vincent noticed something I had not paid much attention to and it caused me to >>>run a few >>>tests to see what was going on. He noticed that the two-thread NPS was _way_ >>>less than >>>what it should be. Here is what I tried. >>> >>>First, on my old quad 700, I first ran a single instance of Crafty on a single >>>test position >>>to get the NPS. I re-ran it immediately to be sure that the initial paging >>>startup did not >>>affect the number. >>> >>>I then ran two instances of crafty on the same position, to see if two >>>independent threads >>>slow things down at all. >>> >>>Finally I ran a two-thread run on the same position to see what happened to the >>>NPS there. >>> >>>I repeated this experiment on my dual 2.8 with hyper-threading disabled in the >>>BIOS so >>>that linux thinks there are two cpus, not four. >>> >>>Here is what I found: >>> >>>On my dual 2.8, a single thread gets 1009K nodes per second on this particular >>>position. >>>Running two separate processes drops this to 993K which is minimal. This means >>>that >>>the two processors are not running into each other trying to get to memory, for >>>example. >>>Finally I got 1529K when running two threads, where the reasonable number would >>>be >>>very close to 2000K. >>> >>>On my quad 700, a single thread gets 284K nodes per second, two separate >>>processes get >>>284K each, and the parallel run with two threads gets 546K. >>> >>>The quad looks perfectly normal and appears to be what I would expect. the dual >>>numbers >>>really seem odd. In fact, the dual numbers look exactly like some of the AMD >>>numbers we >>>discussed a few months back. Except that two separate processes look normal, >>>but one >>>process, two threads is only about 75% of the speed of two separate processes. >>>I'm looking, >>>but I wonder if anyone has any observations? Crafty does very few locks. In >>>these tests, >>>for example, it only did 300 splits which is minimal when compared to the time >>>taken. Since >>>I factor _out_ the time used for splitting and spinning, it would appear that >>>things are simply >>>slowed down because of the shared virtual address space, which doesn't make much >>>sense to >>>me when it works on my quad 700 but fails so badly on the dual 2.8. >>> >>>More as I try to figure out what the hardware is doing... >> >> >>How much RAM of memory do you recommend to have for a dual Dell Xeon 3.06 GHZ? > >The usual answer to this question (without regard to OS) is "How much can you >afford?" > >Matt I am running 4GB on mine but it isn't usefull in chess aand the price has dropped considerably now. 2GB is more than adequate and in shorter games 1GB should be more than sufficient. Sincerely Charles
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