Author: Pavel Blokhine
Date: 14:59:49 04/02/03
Go up one level in this thread
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?
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