[Qemu-devel] [PULL 04/11] memory: Don't update all memory region when ioeventfd changed

[Paolo Bonzini <pbonzini@redhat.com>]

From: Gonglei <arei.gonglei@huawei.com>

memory mappings don't rely on ioeventfds, there is no need
to destroy and rebuild them when manipulating ioeventfds,
otherwise it scarifies performance.

according to testing result, each ioeventfd deleing needs
about 5ms, within which memory mapping rebuilding needs
about 4ms. With many Nics and vmchannel in a VM doing migrating,
there can be many ioeventfds deleting which increasing
downtime remarkably.

Signed-off-by: Gonglei <arei.gonglei@huawei.com>
Signed-off-by: Herongguang <herongguang.he@huawei.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 memory.c | 33 +++++++++++++++++++++++----------
 1 file changed, 23 insertions(+), 10 deletions(-)

diff --git a/memory.c b/memory.c
index 678661e..829d56d 100644
--- a/memory.c
+++ b/memory.c
@@ -28,6 +28,7 @@
 
 static unsigned memory_region_transaction_depth;
 static bool memory_region_update_pending;
+static bool ioeventfd_update_pending;
 static bool global_dirty_log = false;
 
 /* flat_view_mutex is taken around reading as->current_map; the critical
@@ -786,22 +787,34 @@ void memory_region_transaction_begin(void)
     ++memory_region_transaction_depth;
 }
 
+static void memory_region_clear_pending(void)
+{
+    memory_region_update_pending = false;
+    ioeventfd_update_pending = false;
+}
+
 void memory_region_transaction_commit(void)
 {
     AddressSpace *as;
 
     assert(memory_region_transaction_depth);
     --memory_region_transaction_depth;
-    if (!memory_region_transaction_depth && memory_region_update_pending) {
-        memory_region_update_pending = false;
-        MEMORY_LISTENER_CALL_GLOBAL(begin, Forward);
+    if (!memory_region_transaction_depth) {
+        if (memory_region_update_pending) {
+            MEMORY_LISTENER_CALL_GLOBAL(begin, Forward);
 
-        QTAILQ_FOREACH(as, &address_spaces, address_spaces_link) {
-            address_space_update_topology(as);
-        }
+            QTAILQ_FOREACH(as, &address_spaces, address_spaces_link) {
+                address_space_update_topology(as);
+            }
 
-        MEMORY_LISTENER_CALL_GLOBAL(commit, Forward);
-    }
+            MEMORY_LISTENER_CALL_GLOBAL(commit, Forward);
+        } else if (ioeventfd_update_pending) {
+            QTAILQ_FOREACH(as, &address_spaces, address_spaces_link) {
+                address_space_update_ioeventfds(as);
+            }
+        }
+        memory_region_clear_pending();
+   }
 }
 
 static void memory_region_destructor_none(MemoryRegion *mr)
@@ -1373,7 +1386,7 @@ void memory_region_add_eventfd(MemoryRegion *mr,
     memmove(&mr->ioeventfds[i+1], &mr->ioeventfds[i],
             sizeof(*mr->ioeventfds) * (mr->ioeventfd_nb-1 - i));
     mr->ioeventfds[i] = mrfd;
-    memory_region_update_pending |= mr->enabled;
+    ioeventfd_update_pending |= mr->enabled;
     memory_region_transaction_commit();
 }
 
@@ -1406,7 +1419,7 @@ void memory_region_del_eventfd(MemoryRegion *mr,
     --mr->ioeventfd_nb;
     mr->ioeventfds = g_realloc(mr->ioeventfds,
                                   sizeof(*mr->ioeventfds)*mr->ioeventfd_nb + 1);
-    memory_region_update_pending |= mr->enabled;
+    ioeventfd_update_pending |= mr->enabled;
     memory_region_transaction_commit();
 }
 
-- 
1.8.3.1