Author: Bo Persson
Date: 04:30:13 11/09/02
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On November 08, 2002 at 20:59:09, Nolan Denson wrote: > So multithreading chess programs will have a >problem and multi-tasking will see the speedup. This looks like something Vincent would say. :-) Really there is no practical difference between multi-threading and multi-tasking (except for the shared/non-shared address space). >Now what I am wondering is such a thing possible for a chess program? > >Can a program like crafty take some of its threads and do something else that >doesn't use the same register's? The don't use the same registers, that's the real point of this Hyperthreading(TM). Like Bob explains below, the processor have two sets of registers that do not compete, except for memory access and execution resources. For a long time now, the Pentium processors have actually just looked like x86 processors, while they have used an internal execution core to do the real job. The register renaming is just one aspect of this; there are more physical registers than register names, so the connections between a name and a register is changed as needed durinf execution. So there are two distinct parts of the chip, a front end or "Architectual state" which contains the registers and flags that an assembly programmer or a compiler sees, and an execution core (or back end) that does the actual work. They have very little in common; so little that Intel can add a second copy of the "Architectual state" to the chip. The hyperthreading P4s now have two front-ends and one back-end. We knew from before that Intel had some problems fitting the P4 paper design on a limited size chip. This made the P4 a bit unbalanced, making it hard to keep all of its parts busy at all times. Now, with two guys feeding the execution unit it might be easier to keep it busy and get maybe a 20-30% better utilization. Also, with two threads already on-chip, the OS might be able to save some time on expensive task switches. Bo Persson bop2@telia.com
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