commit c67c11b60f7af8f831f42821e1e6953a5bd9c0fe
author Srikant Bharadwaj <srikant.bharadwaj@amd.com> Mon Aug 26 16:41:04 2019 -0400
committer Srikant Bharadwaj <srikant.bharadwaj@amd.com> Tue Sep 03 23:04:31 2019 +0000
tree c1efa2b9a42644d3fe5d32afa0a8ec5d37536558
parent 5cc0db697dc1e3d378178c54dc4905ea8d2a2c8e

ruby: Fix the way stall map size is checked for availability

To ensure that enqueuer observes the practical availability. We
check the message buffer queue size at the start of the cycle.
We also add the size of the stall queue to consider the total
queue size. However, messages can be moved from regular queue
to stall map. This leads to messages being considered twice leading
to false flow control. This patch fixes it by storing the stall map
size at the beginning of the cycle and considering it for checking
availability.

Change-Id: I6ea94f34fe5279b91f74e106d43263e55ec4bf06
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/20389
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>

src/mem/ruby/network/MessageBuffer.cc

diff --git a/src/mem/ruby/network/MessageBuffer.cc b/src/mem/ruby/network/MessageBuffer.cc
index 03d1bb0..f8cab3c 100644
--- a/src/mem/ruby/network/MessageBuffer.cc
+++ b/src/mem/ruby/network/MessageBuffer.cc
@@ -51,6 +51,7 @@
     m_consumer = NULL;
     m_size_last_time_size_checked = 0;
     m_size_at_cycle_start = 0;
+    m_stalled_at_cycle_start = 0;
     m_msgs_this_cycle = 0;
     m_priority_rank = 0;
 
@@ -89,10 +90,12 @@
     // until schd cycle, but enqueue operations effect the visible
     // size immediately
     unsigned int current_size = 0;
+    unsigned int current_stall_size = 0;
 
     if (m_time_last_time_pop < current_time) {
-        // no pops this cycle - heap size is correct
+        // no pops this cycle - heap and stall queue size is correct
         current_size = m_prio_heap.size();
+        current_stall_size = m_stall_map_size;
     } else {
         if (m_time_last_time_enqueue < current_time) {
             // no enqueues this cycle - m_size_at_cycle_start is correct
@@ -102,15 +105,19 @@
             // enqueued msgs to m_size_at_cycle_start
             current_size = m_size_at_cycle_start + m_msgs_this_cycle;
         }
+
+        // Stall queue size at start is considered
+        current_stall_size = m_stalled_at_cycle_start;
     }
 
     // now compare the new size with our max size
-    if (current_size + m_stall_map_size + n <= m_max_size) {
+    if (current_size + current_stall_size + n <= m_max_size) {
         return true;
     } else {
         DPRINTF(RubyQueue, "n: %d, current_size: %d, heap size: %d, "
                 "m_max_size: %d\n",
-                n, current_size, m_prio_heap.size(), m_max_size);
+                n, current_size + current_stall_size,
+                m_prio_heap.size(), m_max_size);
         m_not_avail_count++;
         return false;
     }
@@ -234,6 +241,7 @@
     // adjusted until schd cycle
     if (m_time_last_time_pop < current_time) {
         m_size_at_cycle_start = m_prio_heap.size();
+        m_stalled_at_cycle_start = m_stall_map_size;
         m_time_last_time_pop = current_time;
     }
 
@@ -274,6 +282,7 @@
     m_time_last_time_enqueue = 0;
     m_time_last_time_pop = 0;
     m_size_at_cycle_start = 0;
+    m_stalled_at_cycle_start = 0;
     m_msgs_this_cycle = 0;
 }
 

src/mem/ruby/network/MessageBuffer.hh

diff --git a/src/mem/ruby/network/MessageBuffer.hh b/src/mem/ruby/network/MessageBuffer.hh
index 05821d5..f92d565 100644
--- a/src/mem/ruby/network/MessageBuffer.hh
+++ b/src/mem/ruby/network/MessageBuffer.hh
@@ -192,6 +192,7 @@
     Tick m_last_arrival_time;
 
     unsigned int m_size_at_cycle_start;
+    unsigned int m_stalled_at_cycle_start;
     unsigned int m_msgs_this_cycle;
 
     Stats::Scalar m_not_avail_count;  // count the # of times I didn't have N