> Just to clarify, XDP supports jumbo frames -- i.e. larger than 1500B payload, just not the maximum 9000B size. My personal observation is that many deployments that "require jumbo frames", are usually OK with an of MTU ~3000B. Jumbo frames, yes. Full jumbo frames, no. :-)
Right, that's where my confusion was. My understanding was limited to
"XDP supports jumbo frames" until I got here[1] in the umem
implementation ("computer says no") and started questioning myself.
> Can Alex or Rob explain:
>
> (1) What is your use-case for wanting jumbo-frames?
>
> And (2) will an MTU of ~3000Bytes be sufficient? (which XDP does support)
I don't personally have a need for MTU9K right now. ~3K is totally
sufficient for the usecases I have/know of.
Food for thought, though: I think MTU9K is considered a hard
requirement in the storage space.
Alex Forster
[1]: https://github.com/torvalds/linux/blob/v4.19-rc4/net/xdp/xdp_umem.c#L278
On Thu, Oct 4, 2018 at 2:52 AM Jesper Dangaard Brouer <brouer@xxxxxxxxxx> wrote:
>
> On Thu, 4 Oct 2018 08:44:27 +0200
> Björn Töpel <bjorn.topel@xxxxxxxxx> wrote:
>
> > Den tors 27 sep. 2018 kl 02:56 skrev Rob Sherwood <rob.sherwood@xxxxxxxxx>:
> > >
> > > Thanks for the reference and the page-per-packet point makes sense.
> > > At the same time, not supporting jumbo frames seems like a non-trivial
> > > limitation. Are there a subset of drivers that do support jumbo
> > > frames (or LRO or the other features that require multiple pages per
> > > packet)?
> > >
> >
> > No, not at the moment. XDP has a strict "one frame cannot exceed a
> > page" constraint. Everything that applies to XDP in terms of
> > constraints, applies to AF_XDP as well.
> >
> > Just to clarify, XDP supports jumbo frames -- i.e. larger than 1500B
> > payload, just not the maximum 9000B size. My personal observation is
> > that many deployments that "require jumbo frames", are usually OK with
> > an of MTU ~3000B. Jumbo frames, yes. Full jumbo frames, no. :-)
>
> Thank you for clarifying that Bjørn.
>
> Can Alex or Rob explain:
>
> (1) What is your use-case for wanting jumbo-frames?
>
> And (2) will an MTU of ~3000Bytes be sufficient? (which XDP does support)
>
>
> > > On Tue, Sep 25, 2018 at 9:44 AM Alex Forster <aforster@xxxxxxxxxxxxxx> wrote:
> > > >
> > > > > On my test box running 4.18 if XDP is in use the MTU can not be
> > > > > set higher than 3050.
> > > >
> > > > Ah, that answers a few questions for me. Thanks!
> > > >
> > > > Alex Forster
>
> --
> Best regards,
> Jesper Dangaard Brouer
> MSc.CS, Principal Kernel Engineer at Red Hat
> LinkedIn: http://www.linkedin.com/in/brouer
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