Path: utzoo!mnetor!uunet!husc6!mailrus!ames!oliveb!sun!gorodish!guy
From: guy@gorodish.Sun.COM (Guy Harris)
Newsgroups: comp.arch
Subject: Re: Do RISC Compilers Consider Multipro
Message-ID: <52183@sun.uucp>
Date: 5 May 88 20:31:11 GMT
References: <620@speedy.mcnc.org> <28200140@urbsdc>
Sender: news@sun.uucp
Lines: 15

> Agree with your concern - many RISCs, especially those with register 
> windows, have greatly increased context switch penalties.

Note that while a particular based machine, running a particular version
of a particular operating system, may have a higher context switch time than
a different machine, this may not necessarily be due primarily to the first
machine having lots more registers.

For example, the current virtual-address-cache Sun machines spend lots of their
context-switch time flushing the old U page from the cache (I think this was
mentioned in one of the Usenix or EUUG papers on the new SunOS 4.0 virtual
memory system).  Even on Sun-4s, this time substantially dominates the
register-window-flush time.  Arranging to have the U area at different virtual
addresses in different processes will probably be a much bigger win than
getting rid of the register windows.