KVM: Reduce atomic operations on vcpu->requests
Usually the vcpu->requests bitmap is sparse, so a test_and_clear_bit() for
each request generates a large number of unneeded atomics if a bit is set.
Replace with a separate test/clear sequence. This is safe since there is
no clear_bit() outside the vcpu thread.
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index c8a9d62..e820eb5 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -636,7 +636,12 @@
static inline bool kvm_check_request(int req, struct kvm_vcpu *vcpu)
{
- return test_and_clear_bit(req, &vcpu->requests);
+ if (test_bit(req, &vcpu->requests)) {
+ clear_bit(req, &vcpu->requests);
+ return true;
+ } else {
+ return false;
+ }
}
#endif