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Message-ID: <b0f3d278-5da3-4ef8-8b9b-2cb439e2e88f@gmx.net>
Date: Tue, 17 Oct 2023 16:38:49 +0200
From: Stefan Wahren <wahrenst@....net>
To: Eric Dumazet <edumazet@...gle.com>, "David S . Miller"
<davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, eric.dumazet@...il.com,
Neal Cardwell <ncardwell@...gle.com>
Subject: Re: [PATCH net] tcp: tsq: relax tcp_small_queue_check() when rtx
queue contains a single skb
Hi,
Am 17.10.23 um 14:45 schrieb Eric Dumazet:
> In commit 75eefc6c59fd ("tcp: tsq: add a shortcut in tcp_small_queue_check()")
> we allowed to send an skb regardless of TSQ limits being hit if rtx queue
> was empty or had a single skb, in order to better fill the pipe
> when/if TX completions were slow.
>
> Then later, commit 75c119afe14f ("tcp: implement rb-tree based
> retransmit queue") accidentally removed the special case for
> one skb in rtx queue.
>
> Stefan Wahren reported a regression in single TCP flow throughput
> using a 100Mbit fec link, starting from commit 65466904b015 ("tcp: adjust
> TSO packet sizes based on min_rtt"). This last commit only made the
> regression more visible, because it locked the TCP flow on a particular
> behavior where TSQ prevented two skbs being pushed downstream,
> adding silences on the wire between each TSO packet.
>
> Many thanks to Stefan for his invaluable help !
>
just some figures using my ARM platform (Tarragon) as iperf client and a
PC (Ubuntu 22.04) as iperf server.
Using current net ( 95535e37e895 ) without the patch
# iperf -t 10 -i 1 -c 192.168.1.129
------------------------------------------------------------
Client connecting to 192.168.1.129, TCP port 5001
TCP window size: 96.2 KByte (default)
------------------------------------------------------------
[ 3] local 192.168.1.12 port 33152 connected with 192.168.1.129 port 5001
[ ID] Interval Transfer Bandwidth
[ 3] 0.0- 1.0 sec 10.1 MBytes 84.9 Mbits/sec
[ 3] 1.0- 2.0 sec 9.62 MBytes 80.7 Mbits/sec
[ 3] 2.0- 3.0 sec 9.62 MBytes 80.7 Mbits/sec
[ 3] 3.0- 4.0 sec 9.62 MBytes 80.7 Mbits/sec
[ 3] 4.0- 5.0 sec 9.62 MBytes 80.7 Mbits/sec
[ 3] 5.0- 6.0 sec 9.62 MBytes 80.7 Mbits/sec
[ 3] 6.0- 7.0 sec 9.62 MBytes 80.7 Mbits/sec
[ 3] 7.0- 8.0 sec 9.75 MBytes 81.8 Mbits/sec
[ 3] 8.0- 9.0 sec 9.62 MBytes 80.7 Mbits/sec
[ 3] 9.0-10.0 sec 10.0 MBytes 83.9 Mbits/sec
[ 3] 0.0-10.0 sec 97.2 MBytes 81.5 Mbits/sec
Using current net with applied patch
# iperf -t 10 -i 1 -c 192.168.1.129
------------------------------------------------------------
Client connecting to 192.168.1.129, TCP port 5001
TCP window size: 96.2 KByte (default)
------------------------------------------------------------
[ 3] local 192.168.1.12 port 32854 connected with 192.168.1.129 port 5001
[ ID] Interval Transfer Bandwidth
[ 3] 0.0- 1.0 sec 11.5 MBytes 96.5 Mbits/sec
[ 3] 1.0- 2.0 sec 11.4 MBytes 95.4 Mbits/sec
[ 3] 2.0- 3.0 sec 11.2 MBytes 94.4 Mbits/sec
[ 3] 3.0- 4.0 sec 11.1 MBytes 93.3 Mbits/sec
[ 3] 4.0- 5.0 sec 11.2 MBytes 94.4 Mbits/sec
[ 3] 5.0- 6.0 sec 11.2 MBytes 94.4 Mbits/sec
[ 3] 6.0- 7.0 sec 11.1 MBytes 93.3 Mbits/sec
[ 3] 7.0- 8.0 sec 11.2 MBytes 94.4 Mbits/sec
[ 3] 8.0- 9.0 sec 11.2 MBytes 94.4 Mbits/sec
[ 3] 9.0-10.0 sec 11.2 MBytes 94.4 Mbits/sec
[ 3] 0.0-10.0 sec 113 MBytes 94.4 Mbits/sec
Thanks
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