mem-ruby: Reduce handshaking between CorePair and dir #1117
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FYI, I may not get to this until next week |
@NSurawar has changes to make from my suggestions already, so no worries. |
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@NSurawar can you please wrap the changes up this week? |
Currently when data is downgraded by MOESI_AMD_Base-CorePair (e.g. due to a replacement) this requires a 4-way handshake between the CorePair and the dir. Specifically, the CorePair send a message telling the dir it'd like to downgrade then, the dir sends an ACK back and then, the CorePair writes the data back, and finally, the dir ACKs the writeback. This is very inefficient and not representative of how modern protocols downgrade a request. Accordingly, this commits updates the downgrade support such that the CorePair writes back the data immediately and then the dir ACKs it. Thus, this approach requires only a 2-way handshake. Change-Id: I7ebc85bb03e8ce46a8847e3240fc170120e9fcd6
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@NSurawar : you'll also need to update this branch to the head of develop before this can be committed. |
| //Deprecated - WriteBack data (wb_data) is now sent with VicDirty itself | ||
| //Leaving this in for reference | ||
| assert(0); |
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I would just remove this. The error below should tell you which message type is missing
| @@ -2427,19 +2426,16 @@ machine(MachineType:CorePair, "CP-like Core Coherence") | |||
| } | |||
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| transition(MO_I, NB_AckWB, I) {L2TagArrayWrite} { | |||
| wb_data; | |||
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Remove the wb_data action since these are the only 4 cases it is used
| p_popRequestQueue; | ||
| } | ||
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| transition(BL, {VicDirty, VicClean}) { | ||
| zz_recycleRequestQueue; | ||
| } | ||
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| //CPUData is now deprecated |
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Should remove the CPUData event, in_port triggers, and all CPUData transitions if that is the case
| @@ -1397,22 +1400,33 @@ machine(MachineType:Directory, "AMD Baseline protocol") | |||
| p_popRequestQueue; | |||
| } | |||
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| transition(U, VicDirty, BL) {L3TagArrayRead} { | |||
| transition(U, VicDirty, U) {L3TagArrayRead, L3DataArrayWrite} { | |||
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The 3rd transition , U is not necessary here (it will remain in the same state)
| p_popRequestQueue; | ||
| } | ||
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| transition(U, VicClean, BL) {L3TagArrayRead} { | ||
| transition(U, VicClean, U) {L3TagArrayRead, L3DataArrayWrite} { |
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Also do not need 3rd parameter here
Currently when data is downgraded by MOESI_AMD_Base-CorePair (e.g. due to a replacement) this requires a 4-way handshake between the CorePair and the dir. Specifically, the CorePair send a message telling the dir it'd like to downgrade then, the dir sends an ACK back and then, the CorePair writes the data back, and finally, the dir ACKs the writeback.
This is very inefficient and not representative of how modern protocols downgrade a request. Accordingly, this commits updates the downgrade support such that the CorePair writes back the data immediately and then the dir ACKs it.
Thus, this approach requires only a 2-way handshake.
Change-Id: I7ebc85bb03e8ce46a8847e3240fc170120e9fcd6