Re: NETIF_F_SG question

[Jeff Garzik]

Joakim Tjernlund wrote:
> I am thinking of implementing harware scatter/gatter support( NETIF_F_SG) in my 
> ethernet driver. The network device cannot do HW checksuming.
> 
> Will the IP stack make use of the SG support and will there be any significant performance
> improvement?

No; you need HW checksumming for NETIF_F_SG to be useful.

If HW checksumming is not available, scatter-gather is useless, because 
the net stack must always make a pass over the data to checksum it. 
Since it must do that, it can linearize the skb at the same time, 
eliminating the need for SG.

	Jeff