Re: Realtime Ada Conferences

[lph@sei.cmu.edu (Larry Howard)]

In article <4jdcfd$7gc@news2.delphi.com> tmoran@bix.com writes:
>>Note that these context switch times are for simulated context switching
>>(i.e. threads simulation), rather than for use of operating systems
><flame on>
>  Is it just me, or does calling this a 'simulated context switch'
>remind others of Orwellian language redefinition.  A 'context switch'
>means a switch to a different Ada task.  If an implementation wants to
>include switching OS threads, or rebooting to a different OS, or
>switching to a different computer in orbit on the other side of the
>globe, fine, but don't redefine that as a context switch and anything
>else as 'simulated'.  Especially in a context discussing whether a
>'context switch' takes more than 20 us in a language designed for
>embedded systems.
><flame off>

Tasking implementors, and sometimes Ada programmers, need to
differentiate between tasking implementation alternatives that
exhibit differing performance properties, including context
switching times.  I took Robert's adjectival use of "simulated"
in the above quote to be no more than a designation of a
particular implementation alternative.

Also, a "context switch" need not refer to a switch to a
_different_ task.  More generally, it refers to the invocation
of the scheduler to select a task to run, which may be the same
task that caused the scheduling event.  Excluding this
possibility means that you would need another label for what is
essentially the same metric.  A better definition of context
switching time is the elapsed time between a scheduling event
and the execution of a particular task.
--
Larry Howard
Software Engineering Institute, Carnegie Mellon University
lph@sei.cmu.edu (NeXT Mail OK)      (412) 268-6397