[coyotos-dev] Capability copying

[Jonathan S. Shapiro]

Looks like this bounced the first time...


Charlie may be right that fabricating and destroying resume capabilities
probably does not introduce a cache miss. I am not convinced about this.
The resume capability being formed points to the currently running
process, and at the time of formation the object header of that process
(to which the link pointers point) is not yet in cache. However, let us
assume that I am incorrect.
        
The unlinking and voiding of resume capabilities works the same way in
EROS that it did in CapROS and KeyKOS. Coyotos is not using a link chain
at all, and works very differently.
        
It is still the case that the capability slot being *overwritten* tends
to be prepared and stale, and that this causes cache misses. It is also
the case that the capability copy loop in the invocation path must make
a data-dependent control flow decision that about this that is mostly
predicted wrong.
        
HOWEVER
        
This is only half the story. It remains to be determined whether the
Coyotos approach will, in practice, reduce the total number of cache
misses.
        
I suppose that we will have to see.