From: hjstein@bfr.co.il (Harvey J. Stein) Newsgroups: comp.lang.fortran,comp.parallel.pvm Subject: Re: fortran77 programming Date: 06 Dec 1998 17:24:55 +0200 Organization: Unspecified Organization Message-Id: References: <3660D892.E1EDBF12@est.it> <3665044D.A0F57E59@kings.uq.edu.au> <3665E491.7993355@flash.net> Cc: hjstein@bfr.co.il Xref: ukc comp.lang.fortran:61876 comp.parallel.pvm:7841 Craig Burley writes: > hjstein@bfr.co.il (Harvey J. Stein) writes: > > > Craig Burley writes: > > > > > In this case, the real-time-critical thread needs only half of the > > > single-CPU's time to be serviced according to its scheduling needs > > > (else it couldn't meet those needs on the dual-CPU system). The > > > other half of the time can be used to service the timesharing > > > system generally, and the "slower process" specifically. > > > > This is not the case because of context switch overhead. I might have quoted the wrong paragraph. I meant this in response to the comment that an N times faster CPU is a win over N CPUs. > I didn't say anything about a context-switch occurring. You simply > interleave instructions, if necessary. The single processor machine still has more instructions to execute because of the context switches needed for multitasking. > Remember, *all else is equal*. The double-speed processor has twice > the "fast" registers as the single-speed processor in the dual-processor > has, to make up for the fact that there are, effectively, twice as > many fast registers available. Same for I/O ports, cache, whatever > else you might try to invoke to fortify the spurious claim that > a dual-processor system will be able to do "some tasks" better than the > "equivalent" single-processor system. That's not what anyone ever compares when comparing 1 X mhz CPU vs N X/N mhz CPUs. -- Harvey J. Stein BFM Financial Research hjstein@bfr.co.il