Re: [Gems-users] MOESI_CMP_directory

[Mike Marty <mikem@xxxxxxxxxxx>]

> -By looking at the source code (e.g. MOESI_CMP_directory-L1cache.sm), I see there is neither Exclusive nor Invalid state implemented. Why is that?

Idle == Invalid

The E-state is implemented as M and MM.  An exclusive response goes from
IS-->M.  A store then transitions to MM.

> -There is no transient state to the extra states M_W, MM, and MM_W. Are the extra states never used?

M_W and MM_W are "waiting" states to ensure that a processor is able to
use the block before using permissions.  They really aren't needed for the
protocol because the blocking logic accomplishes the same thing, but I
added them to be consistent with MOESI_CMP_token

> -Is there a state transition diagram for the MOESI_CMP_directory protocol? It would really help to understand the protocol and the source code.

Sorry, no state-transition diagram.

> -It is said that this protocol uses non-inclusive L1/L2 caching with blocking caches. Could somebody please elaborate?
>

A cache "blocks" when handling a request.  Therefore subsequent requests
are queued up instead of NACKed.

--Mike