> I tried to follow the solution that was posted and now run into a
> transition error in which the Owner receives a GETS_LAST_token message.
>
> Shouldn't in the transition proposed in the solution also include the
> Owner state, such that if the Owner has just one token left, he would
> not give it away ?
>
Yes.
The owner running out of tokens isn't a good thing because then the
last Owner is continually passed around (while the responder loses
read permission).
I didn't code up MOESI_SMP_token, but my guess is that this is what is
happening: Sharers get tokens and then eventually replace them to
memory. Memory eventually has all the tokens except the owner. It
then doesn't respond to GETS requests because it isn't the owner. I
bet this is what is happening. If so, my suggestion is to change
memory controller such that it responds to any GETS with tokens (but
without the data...the owner will take care of that).
This is yet another example where the nice "academic simplicity" of
token coherence rears its ugly head when dealing with implementation
details...
--Mike
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