KVM: Calculate available entries in coalesced mmio ring

Instead of checking whether we'll wrap around, calculate how many entries are available, and check whether we have enough (just one) for the pending mmio. By itself, this doesn't change anything, but it paves the way for making this function lockless. Signed-off-by: Avi Kivity <[email protected]>
kernel-patches · Sep 10, 2009 · 105f8d4 · 105f8d4
1 parent 596ae89
commit 105f8d4
Showing 1 changed file with 5 additions and 5 deletions.
diff --git a/virt/kvm/coalesced_mmio.c b/virt/kvm/coalesced_mmio.c
@@ -24,7 +24,8 @@ static int coalesced_mmio_in_range(struct kvm_io_device *this,
 {
 	struct kvm_coalesced_mmio_dev *dev = to_mmio(this);
 	struct kvm_coalesced_mmio_zone *zone;
-	int next;
+	struct kvm_coalesced_mmio_ring *ring;
+	unsigned avail;
 	int i;
 
 	if (!is_write)
@@ -40,10 +41,9 @@ static int coalesced_mmio_in_range(struct kvm_io_device *this,
 	 * check if we don't meet the first used entry
 	 * there is always one unused entry in the buffer
 	 */
-
-	next = (dev->kvm->coalesced_mmio_ring->last + 1) %
-							KVM_COALESCED_MMIO_MAX;
-	if (next == dev->kvm->coalesced_mmio_ring->first) {
+	ring = dev->kvm->coalesced_mmio_ring;
+	avail = (ring->first - ring->last - 1) % KVM_COALESCED_MMIO_MAX;
+	if (avail < 1) {
 		/* full */
 		return 0;
 	}