[coyotos-dev] Activations

[Jonathan S. Shapiro]

On Tue, 2007-05-22 at 13:23 -0400, Christopher Nelson wrote:
>         
>         > It also seems like it could induce false sharing between
>         independent
>         > threads and processes, where delays in fault handling by
>         other threads 
>         > or processes could cause those to propagate and slow down
>         groups who's
>         > processing is otherwise unrelated.  Of course, this assumes
>         that you
>         > are using these handlers for various types of notification
>         (like 
>         > memory mapping / etc.)
>         
>         Now that it is clearer how the fault handler works, do you
>         still have
>         this concern?
>         
> 
> No.  It seems that the only concern I would still have is that
> external fault handlers seem very heavy in comparison to activation
> handlers.  Therefore, you are in a space/complexity trade-off.   If
> these critical paths that activation handlers are blocking are so
> systemically significant that using external fault handlers will
> provide a boost sufficient to negate the memory overhead - then I say
> go for it. 

Umm. Chris? The memory overhead of the activation handler is actually
*higher* than the memory overhead of the external handler...

> It's a shame, though.  I was looking forward to using activations as
> lightweight asynchronous event handlers. :-)

How lightweight they are is entirely a function of the hardware
user/supervisor crossing overhead.