Re: TCP acking too fast

From: Mika Liljeberg (
Date: Sun Oct 14 2001 - 06:49:25 EST

Andi Kleen wrote:
> The only special case for PSH in RX left I can is in rcv_mss estimation,
> where is assumes that a packet with PSH set is not full sized.

A packet without PSH should be full size. Assuming the sender implemets
SWS avoidance correctly, this should be a safe enough assumption.

> On further
> look the 2.4 tcp_measure_rcv_mss will never update rcv_mss for packets
> which do have PSH set and in this case cause random ack behaviour depending
> on the initial rcv_mss guess.
> Not very nice; definitely violates the "be conservative what you accept"
> rule. I'm not sure how to fix it, adding a fallback to every-two-packet-add
> would pollute the fast path a bit.

You're right. As far as I can see, it's not necessary to set the
TCP_ACK_PUSHED flag at all (except maybe for SYN-ACK). I'm just writing
a patch to clean this up.

> -Andi


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This archive was generated by hypermail 2b29 : Mon Oct 15 2001 - 21:00:54 EST