Re: [PATCH net-next 7/8] vhost_net: try batch dequing from skb array

[Jason Wang]

On 2017å03æ22æ 22:16, Michael S. Tsirkin wrote:
> On Tue, Mar 21, 2017 at 12:04:46PM +0800, Jason Wang wrote:
> > We used to dequeue one skb during recvmsg() from skb_array, this could
> > be inefficient because of the bad cache utilization and spinlock
> > touching for each packet. This patch tries to batch them by calling
> > batch dequeuing helpers explicitly on the exported skb array and pass
> > the skb back through msg_control for underlayer socket to finish the
> > userspace copying.
> >
> > Tests were done by XDP1:
> > - small buffer:
> >    Before: 1.88Mpps
> >    After : 2.25Mpps (+19.6%)
> > - mergeable buffer:
> >    Before: 1.83Mpps
> >    After : 2.10Mpps (+14.7%)
> >
> > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> > ---
> >   drivers/vhost/net.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++++----
> >   1 file changed, 60 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> > index 9b51989..53f09f2 100644
> > --- a/drivers/vhost/net.c
> > +++ b/drivers/vhost/net.c
> > @@ -28,6 +28,8 @@
> >   #include <linux/if_macvlan.h>
> >   #include <linux/if_tap.h>
> >   #include <linux/if_vlan.h>
> > +#include <linux/skb_array.h>
> > +#include <linux/skbuff.h>
> >   
> >   #include <net/sock.h>
> >   
> > @@ -85,6 +87,7 @@ struct vhost_net_ubuf_ref {
> >   	struct vhost_virtqueue *vq;
> >   };
> >   
> > +#define VHOST_RX_BATCH 64
> >   struct vhost_net_virtqueue {
> >   	struct vhost_virtqueue vq;
> >   	size_t vhost_hlen;
> > @@ -99,6 +102,10 @@ struct vhost_net_virtqueue {
> >   	/* Reference counting for outstanding ubufs.
> >   	 * Protected by vq mutex. Writers must also take device mutex. */
> >   	struct vhost_net_ubuf_ref *ubufs;
> > +	struct skb_array *rx_array;
> > +	void *rxq[VHOST_RX_BATCH];
> > +	int rt;
> > +	int rh;
> >   };
> >   
> >   struct vhost_net {
> > @@ -201,6 +208,8 @@ static void vhost_net_vq_reset(struct vhost_net *n)
> >   		n->vqs[i].ubufs = NULL;
> >   		n->vqs[i].vhost_hlen = 0;
> >   		n->vqs[i].sock_hlen = 0;
> > +		n->vqs[i].rt = 0;
> > +		n->vqs[i].rh = 0;
> >   	}
> >   
> >   }
> > @@ -503,13 +512,30 @@ static void handle_tx(struct vhost_net *net)
> >   	mutex_unlock(&vq->mutex);
> >   }
> >   
> > -static int peek_head_len(struct sock *sk)
> > +static int peek_head_len_batched(struct vhost_net_virtqueue *rvq)
> Pls rename to say what it actually does: fetch skbs

Ok.

> > +{
> > +	if (rvq->rh != rvq->rt)
> > +		goto out;
> > +
> > +	rvq->rh = rvq->rt = 0;
> > +	rvq->rt = skb_array_consume_batched_bh(rvq->rx_array, rvq->rxq,
> > +						VHOST_RX_BATCH);
> A comment explaining why is is -bh would be helpful.

Ok.

Thanks