From: Rob Landley <rlandley@xxxxxxxxxxxxx>
Going indirect for only two buffers isn't likely to be a performance win
because the kmalloc/kfree overhead for the indirect block can't be cheaper
than one extra linked list traversal.
Properly "tuning" the threshold would probably be workload-specific.
(One big downside of not going indirect is extra pressure on the table
entries, and table size varies.) But I think that in the general case,
2 is a defensible minimum?
Signed-off-by: Rob Landley <rlandley@xxxxxxxxxxxxx>
---
drivers/virtio/virtio_ring.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index b0043fb..2b69441 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -173,7 +173,7 @@ int virtqueue_add_buf_gfp(struct virtqueue *_vq,
/* If the host supports indirect descriptor tables, and we have multiple
* buffers, then go indirect. FIXME: tune this threshold */
- if (vq->indirect && (out + in) > 1 && vq->num_free) {
+ if (vq->indirect && (out + in) > 2 && vq->num_free) {
head = vring_add_indirect(vq, sg, out, in, gfp);
if (likely(head >= 0))
goto add_head;
_______________________________________________
Virtualization mailing list
Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
https://lists.linux-foundation.org/mailman/listinfo/virtualization
