gib...@wsu.edu (Gibney, Dave) writes: > In my opinion, back in the day, there as a benefit of going to > fewer/faster engines. But, with a deep drop off a precipice when fewer > reached one. > > Never again will I willingly agree to be on a single CPU machine.
in the past, multiple engines have been beneficial 1) constraining ill-performing tasks, partially compensating for poor resource management software. 2) increasing importance of cache hit ratios ... careful control of task switching can significantly improve cache hit ratios and aggregate throughput. multiple engines can also help poor resource management software minimizing task switches resulting in having to change cache contents each time. large mainframes use to have large penalty going from one processor to two processor (and enormous penalty going to four processors). two processor 370 hardware used to be only 1.8 times single processor (clocks slowed down to handle cross-cache invalidation) and throughput typically rated at 1.3-1.5 times single processor (because of enormous operating system multiprocessor overhead). in the mid-70s, i managed to do some slight of hand where got nearly 2.0 times throughput with two processors (over one processor), it was some superfast operating system pathlength for management of two processors along with careful task switch management ... that improved cache hit ratio improving throughput compensating for the 20% slowdown hardware slowdown (part of it was logically a little like SAPs where I/O interrupt handling could be partially batched on same processor, improving interrupt handling throughput because of cache affinity of the interrupt handler and improving cache hit ratio of applications on the other processor with fewer interrupts). -- virtualization experience starting Jan1968, online at home since Mar1970 ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN