Re: [MirageOS-devel] TCP checksum offload with Xen

[Thomas Leonard <talex5@xxxxxxxxx>]

On 19 August 2014 11:18, Anil Madhavapeddy <anil@xxxxxxxxxx> wrote:
>
> On 19 Aug 2014, at 05:08, Thomas Leonard <talex5@xxxxxxxxx> wrote:
>
>> I see Xen allows guests to indicate that the packet checksum is blank
>> (XEN_NETTXF_csum_blank). Then dom0 will either fill it in itself or
>> get the NIC to do it. How can I use this with Mirage?
>>
>> I tried using ~flags:3 (Checksum_blank + Data_validated) in
>> mirage-net-xen's netif.ml, but I don't see any TCP packets at all this
>> way, even when the checksum is actually still being set. DHCP still
>> works, though.
>>
>> Does anyone know how this is supposed to work?
>
> Probably best to trace through what netback is doing here:
> http://lxr.free-electrons.com/source/drivers/net/xen-netback/netback.c#L1580
>
> Looks like XEN_NETTXF_data_validated may need to be set as well
> (and local packets are treated differently from off-host ones, to
> add an extra twist).

The problem turned out to be that I was setting the flag for all
packets, including ARPs.
Getting this to work properly will require so API changes, because
NETWORK needs to tell the ethernet driver which types of packet can be
offloaded, and let the driver say which packets require checksums to
be added.

Then similar changes are needed to ETHIF. Here are the hacks I used to test it:

https://github.com/talex5/mirage/commits/csum-offload
https://github.com/talex5/mirage-net-xen/commits/csum-offload
https://github.com/talex5/mirage-tcpip/commits/csum-offload


-- 
Dr Thomas Leonard        http://0install.net/
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