kvm: skip system call when msi route is unchanged

Some guests do a large number of mask/unmask
calls which currently trigger expensive route update
system calls.
Detect that route in unchanged and skip the system call.

Reported-by: "Zhanghaoyu (A)" <haoyu.zhang@huawei.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/kvm-all.c b/kvm-all.c
index 745b5017a1..3ee0ac7e7b 100644
--- a/kvm-all.c
+++ b/kvm-all.c
@@ -1034,6 +1034,10 @@ static int kvm_update_routing_entry(KVMState *s,
             continue;
         }
 
+        if(!memcmp(entry, new_entry, sizeof *entry)) {
+            return 0;
+        }
+
         *entry = *new_entry;
 
         kvm_irqchip_commit_routes(s);