Author: Matthew White
Date: 19:07:39 04/02/03
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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
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