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SubjectRe: unnecessary retransmit from network stack
"David S. Miller" wrote:
>
> From: Christian Widmer <cwidmer@iiic.ethz.ch>
> Date: Fri, 5 Oct 2001 14:29:53 +0200
>
> why does net_dev.hard_start_xmit get called multiple times
> with the same tcp packet?
>
> Because the ACK is not coming back for those packets within the RTO
> (which for a local network is very low). Check your TCP dumps,
> the ACKs of the original data packets are being dropped in transit.

Well, TCP certainly shouldn't be sending two retransmissions
back-to-back within 2ms, especially with nothing received in between.
Not with RTO (which in Linux is never below 20ms, and according to RFC
should be conservatively rounded up to 1 second), nor with fast
retransmits or SACK.

Just an observation.

MikaL
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