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    SubjectRe: txqueuelen has wrong units; should be time
    On Mon, Feb 28, 2011 at 4:45 PM, John Heffner <> wrote:
    > On Mon, Feb 28, 2011 at 11:55 AM, John W. Linville
    > <> wrote:
    >> On Mon, Feb 28, 2011 at 05:48:14PM +0100, Eric Dumazet wrote:
    >>> Le lundi 28 février 2011 à 11:11 -0500, John W. Linville a écrit :
    >>> > On Sun, Feb 27, 2011 at 09:07:53PM +0100, Eric Dumazet wrote:

    >>> > > Qdisc should return to caller a good indication packet is queued or
    >>> > > dropped at enqueue() time... not later (aka : never)
    >>> > >
    >>> > > Accepting a packet at t0, and dropping it later at t0+limit without
    >>> > > giving any indication to caller is a problem.
    >>> >
    >>> > Can you elaborate on what problem this causes?  Is it any worse than
    >>> > if the packet is dropped at some later hop?
    >>> >
    >>> > Is there any API that could report the drop to the sender (at
    >>> > least a local one) without having to wait for the ack timeout?
    >>> > Should there be?
    >>> Not all protocols have ACKS ;)
    >>> dev_queue_xmit() returns an error code, some callers use it.
    >> Well, OK -- I agree it is best if you can return the status at
    >> enqueue time.  The question becomes whether or not a dropped frame
    >> is worse than living with high latency.  The answer, of course, still
    >> seems to be a bit subjective.  But, if the admin has determined that
    >> a link should be low latency...?
    > Notably, TCP is one caller that uses the error code.  The error code
    > is functionally equivalent to ECN, one of whose great advantages is
    > reducing delay jitter.  If TCP didn't get the error, that would
    > effectively double the latency for a full window of data, since the
    > dropped segment would not be retransmitted for an RTT.

    It sounds like you need a callback or similar, so that TCP can be
    informed later that the drop has occurred.
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