Author: Robert Hyatt
Date: 20:07:08 04/07/03
Go up one level in this thread
On April 07, 2003 at 21:18:48, Charles Worthington wrote: >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 4 gigs is actually a bit of a problem. Due to the way the operating systems map themselves into the virtual address space. This introduces a problem on the X86 architecture.
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