MESI: Add queues for stalled requests

This patch adds support for stalling the requests queued up at different
controllers for the MESI CMP directory protocol. Earlier the controllers
would recycle the requests using some fixed latency. This results in
younger requests getting serviced first at times, and can result in
starvation. Instead all the requests that need a particular block to be
in a stable state are moved to a separate queue, where they wait till
that block returns to a stable state and then they are processed.

1 files changed, 28 insertions, 14 deletions

diff --git a/src/mem/protocol/MESI_CMP_directory-L2cache.sm b/src/mem/protocol/MESI_CMP_directory-L2cache.sm
index 16c5bc5a1..9cc20f8c3 100644
--- a/src/mem/protocol/MESI_CMP_directory-L2cache.sm
+++ b/src/mem/protocol/MESI_CMP_directory-L2cache.sm
@@ -158,6 +158,7 @@ machine(L2Cache, "MESI Directory L2 Cache CMP")
   void unset_cache_entry();
   void set_tbe(TBE a);
   void unset_tbe();
+  void wakeUpBuffers(Address a);
 
   // inclusive cache, returns L2 entries only
   Entry getCacheEntry(Address addr), return_by_pointer="yes" {
@@ -283,7 +284,7 @@ machine(L2Cache, "MESI Directory L2 Cache CMP")
   out_port(responseIntraChipL2Network_out, ResponseMsg, responseFromL2Cache);
 
 
-  in_port(L1unblockNetwork_in, ResponseMsg, unblockToL2Cache) {
+  in_port(L1unblockNetwork_in, ResponseMsg, unblockToL2Cache, rank = 2) {
     if(L1unblockNetwork_in.isReady()) {
       peek(L1unblockNetwork_in,  ResponseMsg) {
         Entry cache_entry := getCacheEntry(in_msg.Address);
@@ -305,7 +306,7 @@ machine(L2Cache, "MESI Directory L2 Cache CMP")
   }
 
   // Response IntraChip L2 Network - response msg to this particular L2 bank
-  in_port(responseIntraChipL2Network_in, ResponseMsg, responseToL2Cache) {
+  in_port(responseIntraChipL2Network_in, ResponseMsg, responseToL2Cache, rank = 1) {
     if (responseIntraChipL2Network_in.isReady()) {
       peek(responseIntraChipL2Network_in, ResponseMsg) {
         // test wether it's from a local L1 or an off chip source
@@ -349,7 +350,7 @@ machine(L2Cache, "MESI Directory L2 Cache CMP")
   }
 
   // L1 Request
-  in_port(L1RequestIntraChipL2Network_in, RequestMsg, L1RequestToL2Cache) {
+  in_port(L1RequestIntraChipL2Network_in, RequestMsg, L1RequestToL2Cache, rank = 0) {
     if(L1RequestIntraChipL2Network_in.isReady()) {
       peek(L1RequestIntraChipL2Network_in,  RequestMsg) {
         Entry cache_entry := getCacheEntry(in_msg.Address);
@@ -791,14 +792,17 @@ machine(L2Cache, "MESI Directory L2 Cache CMP")
     }
   }
 
-  action(zz_recycleL1RequestQueue, "zz", desc="recycle L1 request queue") {
-    L1RequestIntraChipL2Network_in.recycle();
+  action(zz_stallAndWaitL1RequestQueue, "zz", desc="recycle L1 request queue") {
+    stall_and_wait(L1RequestIntraChipL2Network_in, address);
   }
 
   action(zn_recycleResponseNetwork, "zn", desc="recycle memory request") {
     responseIntraChipL2Network_in.recycle();
   }
 
+  action(kd_wakeUpDependents, "kd", desc="wake-up dependents") {
+    wakeUpBuffers(address);
+  }
 
   //*****************************************************
   // TRANSITIONS
@@ -820,7 +824,7 @@ machine(L2Cache, "MESI Directory L2 Cache CMP")
   }
 
   transition({IM, IS, ISS, SS_MB, M_MB, MT_MB, MT_IIB, MT_IB, MT_SB}, {L2_Replacement, L2_Replacement_clean}) {
-    zz_recycleL1RequestQueue;
+    zz_stallAndWaitL1RequestQueue;
   }
 
   transition({IM, IS, ISS, SS_MB, M_MB, MT_MB, MT_IIB, MT_IB, MT_SB}, MEM_Inv) {         
@@ -833,7 +837,7 @@ machine(L2Cache, "MESI Directory L2 Cache CMP")
 
 
   transition({SS_MB, M_MB, MT_MB, MT_IIB, MT_IB, MT_SB}, {L1_GETS, L1_GET_INSTR, L1_GETX, L1_UPGRADE}) {
-    zz_recycleL1RequestQueue;
+    zz_stallAndWaitL1RequestQueue;
   }
 
 
@@ -885,6 +889,7 @@ machine(L2Cache, "MESI Directory L2 Cache CMP")
     e_sendDataToGetSRequestors;
     s_deallocateTBE;
     o_popIncomingResponseQueue;
+    kd_wakeUpDependents;
   }
 
   transition(IM, Mem_Data, MT_MB) {
@@ -902,11 +907,11 @@ machine(L2Cache, "MESI Directory L2 Cache CMP")
   }
 
   transition({IS, ISS}, L1_GETX) {
-    zz_recycleL1RequestQueue;
+    zz_stallAndWaitL1RequestQueue;
   }
 
   transition(IM, {L1_GETX, L1_GETS, L1_GET_INSTR}) {
-    zz_recycleL1RequestQueue;
+    zz_stallAndWaitL1RequestQueue;
   }
 
   // transitions from SS
@@ -1018,30 +1023,35 @@ machine(L2Cache, "MESI Directory L2 Cache CMP")
   // transitions from blocking states
   transition(SS_MB, Unblock_Cancel, SS) {
     k_popUnblockQueue;
+    kd_wakeUpDependents;
   }
 
   transition(MT_MB, Unblock_Cancel, MT) {
     k_popUnblockQueue;
+    kd_wakeUpDependents;
   }
 
   transition(MT_IB, Unblock_Cancel, MT) {
     k_popUnblockQueue;
+    kd_wakeUpDependents;
   }
 
   transition(SS_MB, Exclusive_Unblock, MT) {
     // update actual directory
     mmu_markExclusiveFromUnblock;
     k_popUnblockQueue;
+    kd_wakeUpDependents;
   }
 
   transition({M_MB, MT_MB}, Exclusive_Unblock, MT) {
     // update actual directory
     mmu_markExclusiveFromUnblock;
     k_popUnblockQueue;
+    kd_wakeUpDependents;
   }
   
   transition(MT_IIB, {L1_PUTX, L1_PUTX_old}){
-    zz_recycleL1RequestQueue;
+    zz_stallAndWaitL1RequestQueue;
   }
 
   transition(MT_IIB, Unblock, MT_IB) {
@@ -1057,16 +1067,18 @@ machine(L2Cache, "MESI Directory L2 Cache CMP")
   transition(MT_IB, {WB_Data, WB_Data_clean}, SS) {
     m_writeDataToCache;
     o_popIncomingResponseQueue;
+    kd_wakeUpDependents;
   }
 
   transition(MT_SB, Unblock, SS) {
     nnu_addSharerFromUnblock;
     k_popUnblockQueue;
+    kd_wakeUpDependents;
   }
 
   // writeback states
   transition({I_I, S_I, MT_I, MCT_I, M_I}, {L1_GETX, L1_UPGRADE, L1_GETS, L1_GET_INSTR}) {
-    zz_recycleL1RequestQueue;
+    zz_stallAndWaitL1RequestQueue;
   }
 
   transition(I_I, Ack) {
@@ -1091,7 +1103,7 @@ machine(L2Cache, "MESI Directory L2 Cache CMP")
   }
 
   transition(MCT_I,  {L1_PUTX, L1_PUTX_old}){
-    zz_recycleL1RequestQueue; 
+    zz_stallAndWaitL1RequestQueue; 
   }
   
   // L1 never changed Dirty data
@@ -1101,17 +1113,18 @@ machine(L2Cache, "MESI Directory L2 Cache CMP")
   }
 
   transition(MT_I, {L1_PUTX, L1_PUTX_old}){
-    zz_recycleL1RequestQueue; 
+    zz_stallAndWaitL1RequestQueue; 
   }
 
   // possible race between unblock and immediate replacement
   transition({MT_MB,SS_MB}, {L1_PUTX, L1_PUTX_old}) {
-    zz_recycleL1RequestQueue;
+    zz_stallAndWaitL1RequestQueue;
   }
 
   transition(MT_I, WB_Data_clean, NP) {
     s_deallocateTBE;
     o_popIncomingResponseQueue;
+    kd_wakeUpDependents;
   }
 
   transition(S_I, Ack) {
@@ -1127,5 +1140,6 @@ machine(L2Cache, "MESI Directory L2 Cache CMP")
   transition(M_I, Mem_Ack, NP) {
     s_deallocateTBE;
     o_popIncomingResponseQueue;
+    kd_wakeUpDependents;
   }
 }