commit ff5aafa1e9e452061b7e63805ee1d611ed6ce9d9
author Tiago Mück <tiago.muck@arm.com> Tue Mar 01 18:48:43 2022 -0600
committer Tiago Muck <tiago.muck@arm.com> Wed Jun 01 15:23:47 2022 +0000
tree 6b84e946ecf22f3bd6bce384f5094068f01f1d10
parent 041cc658995014bec5926583ea8366b8354d296d

mem-ruby: fix CHI wrong response to ReadShared

When an exclusive cache is responding to a ReadShared and the line is
unique, it send the data in unique state without checking if the line
already has other sharers in other upstream caches.

This patch fixes this issue and also cleans up Send_CompData.

JIRA: https://gem5.atlassian.net/browse/GEM5-1195

Change-Id: Ica7c2afafb55750681b39ae7de99a665689ecb8a
Signed-off-by: Tiago Mück <tiago.muck@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/57389
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>

src/mem/ruby/protocol/chi/CHI-cache-actions.sm

diff --git a/src/mem/ruby/protocol/chi/CHI-cache-actions.sm b/src/mem/ruby/protocol/chi/CHI-cache-actions.sm
index 280ae50..7dbb05c 100644
--- a/src/mem/ruby/protocol/chi/CHI-cache-actions.sm
+++ b/src/mem/ruby/protocol/chi/CHI-cache-actions.sm
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021 ARM Limited
+ * Copyright (c) 2021-2022 ARM Limited
  * All rights reserved
  *
  * The license below extends only to copyright in the software and shall
@@ -2201,27 +2201,15 @@
   bool is_rd_nsd := tbe.reqType == CHIRequestType:ReadNotSharedDirty;
   bool is_rd_unique := tbe.reqType == CHIRequestType:ReadUnique;
 
+  // if the config allows (or not caching the data) and line has no sharers
+  bool snd_unique_on_rs := (fwd_unique_on_readshared || tbe.dataToBeInvalid)
+                          && tbe.dataUnique && tbe.dir_sharers.isEmpty();
+  // if the request type allows and we won't be caching the data
+  bool snd_dirty_on_rs := is_rd_shared && !is_rd_nsd && tbe.dataToBeInvalid;
+
   if (is_rd_once) {
     tbe.snd_msgType := CHIDataType:CompData_I;
-  } else if (tbe.dataToBeInvalid) {
-    // We will drop the data so propagate it's coherent state upstream
-    if (tbe.dataUnique && tbe.dataDirty) {
-      tbe.snd_msgType := CHIDataType:CompData_UD_PD;
-    } else if (tbe.dataUnique) {
-      tbe.snd_msgType := CHIDataType:CompData_UC;
-    } else if (tbe.dataDirty) {
-      if (is_rd_nsd) {
-        tbe.snd_msgType := CHIDataType:CompData_SC;
-      } else {
-        tbe.snd_msgType := CHIDataType:CompData_SD_PD;
-      }
-    } else {
-      tbe.snd_msgType := CHIDataType:CompData_SC;
-    }
-  } else if (is_rd_unique ||
-             (is_rd_shared && tbe.dataUnique &&
-              fwd_unique_on_readshared && (tbe.dir_ownerExists == false))) {
-    // propagates dirtyness
+  } else if (is_rd_unique || (is_rd_shared && snd_unique_on_rs)) {
     assert(tbe.dataUnique);
     if (tbe.dataDirty) {
       tbe.snd_msgType := CHIDataType:CompData_UD_PD;
@@ -2229,8 +2217,13 @@
       tbe.snd_msgType := CHIDataType:CompData_UC;
     }
   } else if (is_rd_shared) {
-    // still keeping a copy so can send as SC
-    tbe.snd_msgType := CHIDataType:CompData_SC;
+    if (tbe.dataDirty && snd_dirty_on_rs) {
+      tbe.snd_msgType := CHIDataType:CompData_SD_PD;
+    } else {
+      // notice the MaintainCoherence will send WriteClean if the line
+      // is dirty and we won't be caching the data
+      tbe.snd_msgType := CHIDataType:CompData_SC;
+    }
   } else {
     error("Invalid request type");
   }