[not speaking for my current employer, but just from past experience ] Certainly a lot of the 'hard' requirements (hard meaning - "without this it won't work") I've seen could be served with a ~3k non-full jumbo frame. But at least what I've seen in the past was that because many of the host-side operations are per-packet limited (e.g., because of CPU or RAM, but ultimately turns into a max pps per host), a trivial way to increase application performance/reduce CPU for networking was to run at as large a frame size as possible. For example, if your application/host is really pps limited, then getting the frame size to increase from 3k to 9k means either 3x more bandwidth for the same cpu usage (assuming the application is bandwidth limited) or 1/3x the CPU usage for the same bandwidth (if the application is not bandwidth limited). Either way, IMHO it's a pretty big win. - Rob . On Thu, Oct 4, 2018 at 12:52 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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