Date: | Fri, 22 Jun 2007 15:31:47 -0400 |
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From: | "Juyoung Jung" <juyoung.jung@xxxxxxxxx> |
Subject: | Re: [Gems-users] Necessity of NP state |
Mike, Your explanation is so helpful for me. Thanks a lot, Mike. By the way, I have another quick question of cache replacement operation. Looking into MESI_SCMP_tiledL2bank_directory- L1cache.sm file, I saw that cache state will change to Invalid state when any cache line in shared(S) or exclusive(M) state encounters L1_Replacement event. However, cache replacement operation should entail getting missed line, and thus I guess the updated line should eventually be marked as non invalid state such as S or M. Please look at the below code from L1 cache controller sm file. For example, for a case of line replacement in M state, state transition will be "Exclusive state --> transient state waiting for ack --> Invalid state" according to transition(M, L1_Replacement, M_I) { i_allocateTBE; g_issuePUTX; // send data, but hold in case forwarded request (but clean data not sent) ff_deallocateL1CacheBlock; } transition(M_I, WB_Ack, I) { s_deallocateTBE; o_popIncomingResponseQueue; } transition(S, L1_Replacement, I) { gs_issuePUTS; ff_deallocateL1CacheBlock; } When the modified cache line to replace receives acknowledgement for write-back completion, it terminates its replacement operation by marking cache line as Invalid. I think further operation may be needed to get new block after receiving WB_Ack; Shouldn't lower-level memory fill the missed line with the required data? (This situation is also shown from cache replacement in S state.) Does Ruby decouple cache line replacement from processor reference such Load and Store? If I have wrong thought, please disabuse me. Thank you. Regards, Young |
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