ref: 21f97338f86b9aa4a2995ddc7bbe539efadfab70
parent: e611879eab9ad99ea6fa1f51529c4c85e679dad2
author: cinap_lenrek <cinap_lenrek@felloff.net>
date: Thu May 14 17:09:12 EDT 2015
tcp: fix loopback slowness issue / set tcb->mss for incoming connections (thanks David du Colombier) David du Colombier wrote: > The slowness issue only appears on the loopback, because > it provides a 16384 MTU. > > There is an old bug in the Plan 9 TCP stack, were the TCP > MSS doesn't take account the MTU for incoming connections. > > I originally fixed this issue in January 2015 for the Plan 9 > port on Google Compute Engine. On GCE, there is an unusual > 1460 MTU. > > The Plan 9 TCP stack defines a default 1460 MSS corresponding > to a 1500 MTU. Then, the MSS is fixed according to the MTU > for outgoing connections, but not incoming connections. > > On GCE, this issue leads to IP fragmentation, but GCE didn't > handle IP fragmentation properly, so the connections > were dropped. > > On the loopback medium, I suppose this is the opposite issue. > Since the TCP stack didn't fix the MSS in the incoming > connection, the programs sent multiple small 1500 bytes > IP packets instead of large 16384 IP packets, but I don't > know why it leads to such a slowdown.