On Thu, 5 Jun 2003, Phillip Hellewell said: > > No, it would run like a single Pentium 4 3GHz. With hyperthreading > > enabled, Linux actually sees two CPUs. So, it completely depends on how > > Do you need to enable something special in the kernel to support this, > or just enable SMP? > > Phillip
Nothing really special needs to be done, other than SMP support. From the OS perspective, two processors are seen. HyperThreading achieves this by duplicating the architecture state (registers, instruction issue unit, etc) of the processor. Both logical processors share the same physical processing units (memory ports, ALU, floating point unit, etc), but they can be more fully allocated because each logical processor schedules use of the processing units. The end result is that if one logical processor is doing some integer operations, the other can utilize the floating point unit (for example). This doesn't always work, since both logical processors may try to use the same processor resources, but will generally provide some speedup in the long run. Probably the biggest benefit out of the whole process is that a 30 percent performance gain [1] can be seen with very little extra silicon (if I remember correctly, my Computer Architecture News said less than 1%). In most circles, that's considered a pretty good gain. If you could get a 30% boost in your salary by working 1% harder, wouldn't you? Th 4 (physical) processor box won't necessarily perform quite as well as an 8-way box, but it will almost definitely outperform a normal 4-way box. The price difference to add HyperThreading is pretty negligable, so it's way cheaper than adding the same amount of actual physical processing. The white paper [2] is a pretty good read. Frank --------------------------------------------------------------------------- Frank Sorenson - KD7TZK CSR Computer Science Department Brigham Young University [EMAIL PROTECTED] [1] http://www.intel.com/eBusiness/products/server/processor/xeon/wp020901_sum.htm?iid=Homepage+htland_ebizxeon&; [2] http://www.intel.com/eBusiness/pdf/prod/server/xeon/wp020901.pdf ____________________ BYU Unix Users Group http://uug.byu.edu/ ___________________________________________________________________ List Info: http://uug.byu.edu/cgi-bin/mailman/listinfo/uug-list
