Re: [Bloat] lwn.net's tcp small queues vs wifi aggregation solved

[Michael Richardson <mcr@sandelman.ca>]

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Jonathan Morton <chromatix99@gmail.com> wrote:
    >>> I would instead frame the problem as "how can we get hardware to
    >>> incorporate extra packets, which arrive between the request and grant
    >>> phases of the MAC, into the same TXOP?"  Then we no longer need to
    >>> think probabilistically, or induce unnecessary delay in the case that
    >>> no further packets arrive.
    >>
    >> I've never looked at the ring/buffer/descriptor structure of the ath9k, but
    >> with most ethernet devices, they would just continue reading descriptors
    >> until it was empty.   Is there some reason that something similar can not
    >> occur?
    >>
    >> Or is the problem at a higher level?
    >> Or is that we don't want to enqueue packets so early, because it's a source
    >> of bloat?

    > The question is of when the aggregate frame is constructed and
    > "frozen", using only the packets in the queue at that instant.  When
    > the MAC grant occurs, transmission must begin immediately, so most
    > hardware prepares the frame in advance of that moment - but how far in
    > advance?

Oh, I understand now.  The aggregate frame has to be constructed, and it's
this frame that is actually in the xmit queue.  I'm guessing that it's in the
hardware, because if it was in the driver, then we could perhaps do something?

    > In principle it should be possible to delay frame construction until
    > the moment the radio is switched on; there is a short period consumed
    > by a data-indepedent preamble sequence.  In the old days, HW designers
    > would have bent over backwards to make that happen.

--
]               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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