Re: [9front] [patch] ethervgbe: add rx checksum offloading

[cinap_lenrek@felloff.net]

sorry, but yes. we have a fast-path where we skip checking the ip header
cheksum if the Block has the flag that says it was already checked
by hardware:

	if((bp->flag & Bipck) == 0 && ipcsum(&h->vihl)) {
		ip->stats[InHdrErrors]++;
		netlog(f, Logip, "%V -> %V: bad ip header checksum\n", h->src, h->dst);
		goto drop;
	}

i cannot say if this is really worth it tho. i have no measured it. and
the ip *HEADER* is not very big and the code in ipcsum() has a fast-path
in itself handling the common fixed header size case.

i would say the complexity of this is very low. all the ethernet driver
needs todo is set a flag on the Block to say hw already calculated the
ip header checksum.

also, we do not memcpy every packet. thats what Block's and Block lists
are about. the ip fragments are stored as lists of packets (with all the
headers) without touching them until it becomes really neccessary.
the Block's are directly filled by hardware dma in the common ethernet
case.

maybe you ment when the payload gets passed to userspace? in that case,
yes, when data is tranferred between userspace and kernel memory it gets
copied. but within the kernel, qio/blocks are avoiding doing that.

--
cinap