From: Michael S. Tsirkin
> On Wed, Oct 15, 2014 at 09:49:01AM +0000, David Laight wrote:
> > From: Of Michael S. Tsirkin
> > > On Wed, Oct 15, 2014 at 03:25:27PM +0800, Jason Wang wrote:
> > > > Accumulate the sent packets and sent bytes in local variables and perform a
> > > > single u64_stats_update_begin/end() after.
> > > >
> > > > Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
> > > > Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
> > > > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> > >
> > > Not sure how much it's worth but since Eric suggested it ...
> >
> > Probably depends on the actual cost of u64_stats_update_begin/end
> > against the likely extra saving of the tx_bytes and tx_packets
> > values onto the stack across the call to dev_kfree_skb_any().
> > (Which depends on the number of caller saved registers.)
>
> Yea, some benchmark results would be nice to see.
I there are likely to be multiple skb on the queue the fastest
code would probably do one 'virtqueue_get_all()' that returned
a linked list of buffers, then follow the list to get the stats,
and follow it again to free the skb.
David
> > > Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> > >
> > > > ---
> > > > drivers/net/virtio_net.c | 12 ++++++++----
> > > > 1 files changed, 8 insertions(+), 4 deletions(-)
> > > >
> > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > > index 3d0ce44..a4d56b8 100644
> > > > --- a/drivers/net/virtio_net.c
> > > > +++ b/drivers/net/virtio_net.c
> > > > @@ -833,17 +833,21 @@ static void free_old_xmit_skbs(struct send_queue *sq)
> > > > unsigned int len;
> > > > struct virtnet_info *vi = sq->vq->vdev->priv;
> > > > struct virtnet_stats *stats = this_cpu_ptr(vi->stats);
> > > > + u64 tx_bytes = 0, tx_packets = 0;
> >
> > tx_packets need only be 'unsigned int'.
> > The same is almost certainly true of tx_bytes.
> >
> > David
> >
> > > > while ((skb = virtqueue_get_buf(sq->vq, &len)) != NULL) {
> > > > pr_debug("Sent skb %p\n", skb);
> > > >
> > > > - u64_stats_update_begin(&stats->tx_syncp);
> > > > - stats->tx_bytes += skb->len;
> > > > - stats->tx_packets++;
> > > > - u64_stats_update_end(&stats->tx_syncp);
> > > > + tx_bytes += skb->len;
> > > > + tx_packets++;
> > > >
> > > > dev_kfree_skb_any(skb);
> > > > }
> > > > +
> > > > + u64_stats_update_begin(&stats->tx_syncp);
> > > > + stats->tx_bytes += tx_bytes;
> > > > + stats->tx_packets =+ tx_packets;
> > > > + u64_stats_update_end(&stats->tx_syncp);
> > > > }
> > > >
> > > > static int xmit_skb(struct send_queue *sq, struct sk_buff *skb)
> > > > --
> > > > 1.7.1
> > > --
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> >
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