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Message-ID: <f4670ce0f4399fe82e7168fb9c491d8eb718e8d8.camel@sipsolutions.net>
Date: Thu, 12 Dec 2019 16:47:30 +0100
From: Johannes Berg <johannes@...solutions.net>
To: Neal Cardwell <ncardwell@...gle.com>
Cc: Eric Dumazet <eric.dumazet@...il.com>,
Toke Høiland-Jørgensen <toke@...hat.com>,
linux-wireless@...r.kernel.org, Netdev <netdev@...r.kernel.org>
Subject: Re: debugging TCP stalls on high-speed wifi
Hi Neal,
On Thu, 2019-12-12 at 10:11 -0500, Neal Cardwell wrote:
> On Thu, Dec 12, 2019 at 9:50 AM Johannes Berg <johannes@...solutions.net> wrote:
> > If you have any thoughts on this, I'd appreciate it.
>
> Thanks for the detailed report!
Well, it wasn't. For example, I neglected to mention that I have to
actually use at least 2 TCP streams (but have tried up to 20) in order
to not run into the gbit link limit on the AP :-)
> I was curious:
>
> o What's the sender's qdisc configuration?
There's none, mac80211 bypasses qdiscs in favour of its internal TXQs
with FQ/codel.
> o Would you be able to log periodic dumps (e.g. every 50ms or 100ms)
> of the test connection using a recent "ss" binary and "ss -tinm", to
> hopefully get a sense of buffer parameters, and whether the flow in
> these cases is being cwnd-limited, pacing-limited,
> send-buffer-limited, or receive-window-limited?
Sure, though I'm not sure my ss is recent enough for what you had in
mind - if not I'll have to rebuild it (it was iproute2-ss190708).
https://p.sipsolutions.net/3e515625bf13fa69.txt
Note there are 4 connections (iperf is being used) but two are control
and two are data. Easy to see the difference really :-)
> o Would you be able to share a headers-only tcpdump pcap trace?
I'm not sure how to do headers-only, but I guess -s100 will work.
https://johannes.sipsolutions.net/files/he-tcp.pcap.xz
Note that this is from a different run than the ss stats.
johannes
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