Re: [Gems-users] question on ack counting

[Mike Marty <mikem@xxxxxxxxxxx>]

> If I add a RAC to MOESI_SMP_directory, and make the rac share the same
> controller with L1/L2, do I need to make sure the RAC is also exclsive to
> the L1/L2?

I haven't thought this completely through, but I would think you could
make it non-exclusive if you wanted.  It might get tricky...see below.

> Here is my concern. If I have a share copy in L2, and a share copy in RAC.
> When other processor asks for the exclusive copy, the follwing transition
> (S->I) will be triggered twice,. Since both RAC and L2 will send an
> invalidation acknoledge, this will definitely confuse the processor which
> does the ack counting. How to make sure only one ack be sent each
> processor?
> transition(S, Inv, I) {
>     f_sendAck;
>     l_popForwardQueue;
>  }
>

Why would the transition trigger twice?  If the global directory treats
each L1/L2/RAC node as a possible sharer, it should only recieve a single
INV message.  Then you have to ensure that every cache indeed gets
invalidated.

Pay close attention to getState and setState and how they might handle a
RAC. In the transition above, you would want to make sure that the State
in both the L1/L2 and RAC both get set to Invalid in the setState()
function.

getState() could check the status of both the L1/L2 caches and the RAC.
If it is present in both, it could return a different state to indicate
this if you wanted.

The choice of integrating a RAC into an L1/L2 controller vs. a seperate
controller is probably not clear.



> BTW, is there any protocol using distributed shared memory, ccNUMA like?
>

Any directory protocol using a Torus-like interconnect is ccNUMA.  However
your Solaris checkpoint likely treats all of memory as UMA.

--Mike