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[Qemu-devel] [PATCH 3/5] kvm: skip system call when msi route is unchang

From: Paolo Bonzini
Subject: [Qemu-devel] [PATCH 3/5] kvm: skip system call when msi route is unchanged
Date: Wed, 3 Jul 2013 10:44:30 +0200

From: "Michael S. Tsirkin" <address@hidden>

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)" <address@hidden>
Signed-off-by: Michael S. Tsirkin <address@hidden>
Signed-off-by: Gleb Natapov <address@hidden>
 kvm-all.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kvm-all.c b/kvm-all.c
index 745b501..3ee0ac7 100644
--- a/kvm-all.c
+++ b/kvm-all.c
@@ -1034,6 +1034,10 @@ static int kvm_update_routing_entry(KVMState *s,
+        if(!memcmp(entry, new_entry, sizeof *entry)) {
+            return 0;
+        }
         *entry = *new_entry;

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