From: Rob Landley <[email protected]> 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 <[email protected]> --- 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 [email protected] https://lists.linux-foundation.org/mailman/listinfo/virtualization
