🚀 go-pugleaf

In article <1RcY6x#64Zq3Y=news@anise.acc.com> lars@salt.acc.com (Lars J Poulsen) writes:

>large a register file is saving and restoring on context switches. While
>interrupt service routines can ignore this and store only what they

From time to time, I have seen the argument that large register files slow
down context switches.  Yes and no.  If you are looking at general purpose
operating systems like Unix, register saves are a very small part of the
cost of a context switch.  Last week I saw an ad for a real time version
of Unix with a guaranteed response time (switch to kernel to high priority
process) of 5 milliseconds.  Now, for the sizes of register files we are
talking about, a register save is about 1/1000th to 1/100th of the total time.

If you are looking at embedded real time systems with no general purpose kernel,
a large number of registers could be a problem.  Where it gets "interesting"
is if you are trying to support microtasking at the outer do-loop level in
Fortran from within the kernel.  Well, there is no such thing as a free lunch.
I guess you just have to design carefully when you get near the edge...

  Hugh LaMaster, m/s 233-9,  UUCP ames!lamaster
  NASA Ames Research Center  ARPA lamaster@ames.arc.nasa.gov
  Moffett Field, CA 94035     
  Phone:  (415)694-6117