Re: [PATCH net-next 6/7] net: dsa: remove useless copy of tagger xmit

From: Andrew Lunn
Date: Tue May 30 2017 - 11:29:49 EST


On Tue, May 30, 2017 at 10:21:30AM -0400, Vivien Didelot wrote:
> The dsa_slave_priv structure holds a copy of the dsa_device_ops xmit
> function. It is always assigned to the switch tree xmit function.
>
> Remove this useless copy.
>
> Signed-off-by: Vivien Didelot <vivien.didelot@xxxxxxxxxxxxxxxxxxxx>
> ---
> net/dsa/dsa_priv.h | 3 ---
> net/dsa/slave.c | 4 +---
> 2 files changed, 1 insertion(+), 6 deletions(-)
>
> diff --git a/net/dsa/dsa_priv.h b/net/dsa/dsa_priv.h
> index 0fdd2a8a4ad8..282a55639285 100644
> --- a/net/dsa/dsa_priv.h
> +++ b/net/dsa/dsa_priv.h
> @@ -71,9 +71,6 @@ struct dsa_device_ops {
> };
>
> struct dsa_slave_priv {
> - struct sk_buff * (*xmit)(struct sk_buff *skb,
> - struct net_device *dev);
> -
> /* DSA port data, such as switch, port index, etc. */
> struct dsa_port *dp;
>
> diff --git a/net/dsa/slave.c b/net/dsa/slave.c
> index 887e26695519..ebad2af4d3a8 100644
> --- a/net/dsa/slave.c
> +++ b/net/dsa/slave.c
> @@ -363,7 +363,7 @@ static netdev_tx_t dsa_slave_xmit(struct sk_buff *skb, struct net_device *dev)
> dev->stats.tx_bytes += skb->len;
>
> /* Transmit function may have to reallocate the original SKB */
> - nskb = p->xmit(skb, dev);
> + nskb = p->dp->ds->dst->tag_ops->xmit(skb, dev);

This is also the hot path for DSA transmit. Do we really want to do 4
extra pointer dereferences a million times per second, compared to one
copy during setup?

Andrew