Author: Robert Hyatt
Date: 19:45:32 12/02/02
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On December 02, 2002 at 20:00:33, Matt Taylor wrote: ><snip> >>I'm more interested in current hardware. IE two 2.8ghz xeons with the E7500 >>chipset >>vs the AMD 2600+/2700+ since they "seem" to be available... > >Wouldn't it be more accurate to test against another SMP system? A single 2.8 >GHz Xeon would contend with an AMD AthlonXP 2700, but using 2 would sway the >odds just a bit I think. Actually, from what I have read and seen, the AthlonXP >2700 can be expected to beat the 2.8 GHz P4 and exceed the 3.0 GHz P4 in some >areas. > Sorry. I was talking about head to head. IE a single vs a single, or a dual vs a dual. No doubt a dual in either cpu would smoke a single in the other... >>I'll post the Intel numbers when the machine arrives, both with and without >>hyper-threading. >>But I believe that the hyper-threading stuff is what is going to make the 2xXeon >>significantly >>faster... Since it seems to help for Crafty and Eugene has not fixed all of the >>spin/loop problems. >>I don't know if he fixed the Lock() asm stuff, but there is another place that >>needs fixing to make >>it really work efficiently. ><snip> > >Does hyper-threading really help that much? It seems like it would create more >contention for limited resources (decoder, internal u-op cache, even some >execution units). I would be extremely interested in seeing hyperthreading >benchmarks with Crafty. First, if you look at the concept of trace-cache, it is _behind_ the decoder, and all it stores are decoded instructions (micro-ops). Since Crafty uses the _same_ code in all threads, it is likely that the shared L1 I-cache (and the L1 D-cache and L2 cache) will all contain stuff that is useful across the two threads... Eugene already ran some and posted the results. The raw NPS went up by a factor of 1.3X. I think more can be had but at a couple of critical places where I have a "busy spin" I need to insert a "pause" asm instruction so that the cpu will work on the thread doing useful work if there is a choice...
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