Re: UDP stress-testing

[Michael Richardson <mcr@sandelman.ca>]

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Alexander Aring <alex.aring@gmail.com> wrote:
    > _All_ current supported transceivers have on hardware side _one_
    > framebuffer only.

    > I would agree 3-4 frames should keep the transmitter buffer, because
    > only one framebuffer, 250kBit (even slower on sub 1-GHz) and holding
    > 3-4 skb's in background.

If we are counting frames rather than packets, then I agree that 3-4 is too
low; we should accomodate 2-3 full-sized IPv6 packets worth of fragments.
1280 / 88 = 14 * 3 = 42.
So I suggest somewhere between 32 and 48 as a good default.

Well, we really ought to use the BQL to get the right number!
        https://lwn.net/Articles/469652/

    > On most systems the qdisc default is pfifo (but I remember something
    > that systemd changed to fq_codel as default).

yes, fq_codel is often the default now.

    > This will getting the queue full and with payload of 352 bytes it makes
    > fragments invalid because pfifo will drop some which is part of the
    > whole fragment.

I had assumed that the fragmentation happened after the qdisc.

    > What I know is, when we drop one fragment, then we could drop every
    > fragment inside the queue which comes from the whole fragmented 6lowpan
    > packet. it seems this will not be handled currently.

This is very important, and why I had assumed that fragmentation was
afterwards.

--
]               Never tell me the odds!                 | ipv6 mesh networks [
]   Michael Richardson, Sandelman Software Works        | network architect  [
]     mcr@sandelman.ca  http://www.sandelman.ca/        |   ruby on rails    [


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