[Tinyos-host-mote-wg] Re: [Tinyos-2.0wg] TOS2 tasks code size

[Cory Sharp]

On 10/8/05, Philip Levis <pal at cs.stanford.edu> wrote:
> On Oct 5, 2005, at 1:00 PM, Cory Sharp wrote:
>
> > One small thing that been bothering me is that TinyOS 2.x tasks
> > compile to slightly larger code than TinyOS 1.x tasks, but my
> > expectation is TOS2 tasks should take the same or less space.  I can't
> > quite figure out where the space is going, and I wonder if anyone else
> > has any ideas as to what's causing the minor bloat.
>
> Hrm. Looking at the code, this doesn't seem totally crazy. The T2
> code is definitely more lines and has more cases. Have you looked at
> the assembly?
>
> When I put the T2 code in there, all I really did was copy your
> example code from reserved tasks. I will take a look on Sunday and do
> a code review pass to see if I can cut the code down. It might be
> useful if we iterated once more after that (you take a look at my
> code and try to cut *it* down).

I've done a pass over it and was only able to make minor improvements.

I was talking to David G about it a couple of days ago.  My intuition
is that the dispatch to the case statements (with inlined task bodies)
should take less space than the sum of per function prelude and
prologue.  But, I think my intuition is wrong.  Though, I'd have to
carefully peruse the assembly code to understand exactly why.

Another experiment could be to mangle an app.c to invoke the tasks
through a static const function pointer array rather than through a
switch statement, and see if that offers any improvement.  If that
helps, that would indicate the dispatch is the place to optimize,
rather than the rest of the scheduler code.

Cory

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