From: jimh@surreal.asd.sgi.com (Jim Helman) Subject: Re: TECH: VR Operating systems and languages Date: Sat, 4 Jul 1992 19:48:54 GMT Organization: Home for Degenerate Physicists In article <1992Jun26.050357.18311@u.washington.edu> Richard A Romano writes: Because of the design of most modern day multiprocessing system, determinism can actually be reduced in multiprocessor systems. An interesting point. In principle, it's certainly possible for the availability of additional CPU resources to allow a process to busy the disk or bus, thereby degrading performance of higher priority tasks. But in practice, if there are other heavy jobs running on the system, you're hosed anyway. And if we're talking about using Unix boxes for real-time, there's no comparison between uniprocessors and multi- processors. On a uniprocessor, worst case timing has to consider clock interrupts, non-preemptable sections of the kernel, not to mention user processes like the window server and network daemons which can get in the way. On a dedicated system, these are the common killers of determinism, not a rogue process going to disk. On an MP system, a process can own a CPU. Under IRIX, it means you can get interrupt response time down to less than 200us for a processor dedicated to a single process. In summary, MP Unix is better for throughput and better for real-time scheduling than 1P Unix. Most VR apps could use a little more of both. regards, -jim jim helman jimh@surreal.asd.sgi.com 415.390.1151