On Mon, Nov 14, 2022 at 4:21 AM Felix Fietkau <nbd@xxxxxxxx> wrote:My issue was the fact that XDP in general (including generic XDP) assumes that packets have 256 bytes of headroom, which is usually only true for drivers that already have proper driver or hardware XDP support.
On 14.11.22 12:55, Vladimir Oltean wrote:
> On Sat, Nov 12, 2022 at 12:13:15PM +0100, Felix Fietkau wrote:
>> On 12.11.22 05:40, Jakub Kicinski wrote:
>> I don't really see a valid use case in running generic XDP, TC and NFT on a
>> DSA master dealing with packets before the tag receive function has been
>> run. And after the tag has been processed, the metadata DST is cleared from
>> the skb.
>
> Oh, there are potentially many use cases, the problem is that maybe
> there aren't as many actual implementations as ideas? At least XDP is,
> I think, expected to be able to deal with DSA tags if run on a DSA
> master (not sure how that applies when RX DSA tag is offloaded, but
> whatever). Marek Behun had a prototype with Marvell tags, not sure how
> far that went in the end:
> https://www.mail-archive.com/netdev@xxxxxxxxxxxxxxx/msg381018.html
> In general, forwarding a packet to another switch port belonging to the
> same master via XDP_TX should be relatively efficient.
In that case it likely makes sense to disable DSA tag offloading
whenever driver XDP is being used.
Generic XDP probably doesn't matter much. Last time I tried to use it
and ran into performance issues, I was told that it's only usable for
testing anyway and there was no interest in fixing the cases that I ran
into.
XDP continues to evolve rapidly, as do its use cases. ( ex:
ttps://github.com/thebracket/cpumap-pping#readme )
What cases did you run into?