Author: Matt Taylor
Date: 18:36:57 12/13/02
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On December 13, 2002 at 11:33:17, Robert Hyatt wrote: <snip> >Regardless of hand-waving nay-sayers. It is a logical development of removing >one more >time-critical piece of code from the Operating System into the microprocessor, >namely the >task scheduler. I wouldn't say that. I opened task manager for a second on my NT box and discovered that I have 324 threads running. For HT to replace the NT task scheduler, it would need the capability to handle at least the 324 concurrent processes I have running now (technically it would need to handle *many* more). I quote the numbers for NT because Unix variants are usually not as prolific with scheduling units, usually because Unix threads/processes aren't very lightweight... HT will not scale to large numbers of tasks. The IA-32 register set has 8 32-bit general registers, 8 80-bit FPU registers, 2 16-bit FPU control registers, and 8 128-bit SSE registers. This means each logical CPU requires 244 bytes of application register file alone. For simplicitly, I did not include the 3 groups of system registers, the MTRRs, or the MSRs. There are additional caches which would not allow HT to scale unless they were duplicated. Intel is not about to put MBs of fast-access register file on an IA-32 processor. It would make your 128-cpu HT Pentium 5 cost more than a cluster of Itaniums with negligible performance gain over a dual- or quad-Xeon system. HT is merely a way to make the existing hardware more efficient. If it were anything more, it would add -additional- hardware registers so the OS could control the scheduling algorithm and specify the location of the ready queue. It would also add instructions that would allow the processor to switch tasks. However, I must agree that multiprocessing and parallel hardware is the future... -Matt
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