On Tue, Feb 11, 2014 at 10:58:52PM +0800, Qin Chuanyu wrote:
> udp packet use 2 buffers at least, one for vnet_hdr and
> one for skb->data.
Not really, we use 1 buffer now with vnet_hdr inline with data.
> we could change the threshold from 2 to 3, so the udp packet
> which data buff only using single desc will gain from this.
> the guest would avoid from allocating memory dynamically.
> the host would avoid from translating indirect desc.
>
> Signed-off-by: Chuanyu Qin <qinchuanyu@xxxxxxxxxx>
Optimization patch without any performance data?
Such a change would need much more testing than that:
would have to try various workloads with -net and -blk at least.
> ---
> drivers/virtio/virtio_ring.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 28b5338..88d008f 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -220,7 +220,7 @@ static inline int virtqueue_add(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 && total_sg > 1 && vq->vq.num_free) {
> + if (vq->indirect && total_sg > 2 && vq->vq.num_free) {
> head = vring_add_indirect(vq, sgs, next, total_sg, total_out,
> total_in,
> out_sgs, in_sgs, gfp);
> --
> 1.7.3.1.msysgit.0
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