commit 529d0cdbfe77a4ad655fe57f2d5320dbb760ef13
author Jason Lowe-Power <jason@lowepower.com> Thu Apr 04 14:10:16 2019 -0700
committer Jason Lowe-Power <jason@lowepower.com> Fri Apr 05 17:36:37 2019 +0000
tree 8c2433849ffe84bf3278140ea9a260e74ace202e
parent 07eca72e1a51910e8ff785c224bf3820183d3664

mem: Reverse order of write/read mem queue check

For atomic RMW instructions that go directly to memory, we want to put
them on the write queue instead of the read queue. Swap the if/else
condition to accomplish this.

Note: This is ignoring the read latency of the RMW, but these
instructions should usually be handled in caches anyway.

Change-Id: I62dbfff3a16ac470f1ebdb489abe878962b20bb6
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/17828
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>

src/mem/dram_ctrl.cc

diff --git a/src/mem/dram_ctrl.cc b/src/mem/dram_ctrl.cc
index dd03cf1..e89a47a 100644
--- a/src/mem/dram_ctrl.cc
+++ b/src/mem/dram_ctrl.cc
@@ -644,21 +644,7 @@
     qosSchedule( { &readQueue, &writeQueue }, burstSize, pkt);
 
     // check local buffers and do not accept if full
-    if (pkt->isRead()) {
-        assert(size != 0);
-        if (readQueueFull(dram_pkt_count)) {
-            DPRINTF(DRAM, "Read queue full, not accepting\n");
-            // remember that we have to retry this port
-            retryRdReq = true;
-            numRdRetry++;
-            return false;
-        } else {
-            addToReadQueue(pkt, dram_pkt_count);
-            readReqs++;
-            bytesReadSys += size;
-        }
-    } else {
-        assert(pkt->isWrite());
+    if (pkt->isWrite()) {
         assert(size != 0);
         if (writeQueueFull(dram_pkt_count)) {
             DPRINTF(DRAM, "Write queue full, not accepting\n");
@@ -671,6 +657,20 @@
             writeReqs++;
             bytesWrittenSys += size;
         }
+    } else {
+        assert(pkt->isRead());
+        assert(size != 0);
+        if (readQueueFull(dram_pkt_count)) {
+            DPRINTF(DRAM, "Read queue full, not accepting\n");
+            // remember that we have to retry this port
+            retryRdReq = true;
+            numRdRetry++;
+            return false;
+        } else {
+            addToReadQueue(pkt, dram_pkt_count);
+            readReqs++;
+            bytesReadSys += size;
+        }
     }
 
     return true;