linux-kernel - Re: [PATCH] This extends tx_data and and iscsit_do_tx_data with the additional parameter flags and avoids sending multiple TCP packets in iscsit_fe_sendpage

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Date:	Mon, 10 Feb 2014 22:14:45 +0100
From:	Thomas Glanzmann <thomas@...nzmann.de>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>,
	John Ogness <john.ogness@...utronix.de>,
	Eric Dumazet <edumazet@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	target-devel <target-devel@...r.kernel.org>,
	Linux Network Development <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] This extends tx_data and and iscsit_do_tx_data with the
 additional parameter flags and avoids sending multiple TCP packets in
 iscsit_fe_sendpage_sg

Hello Eric,

> Hmm.. I was not aware of high RTT for some packets.
> Can you spot this on the pcap you provided ?

with the latest patch as in:

(node-62) [~/work/linux-2.6] git diff | pbot
http://pbot.rmdir.de/CQwqI6b7wJProw_xaukmEg

with net.ipv4.tcp_min_tso_segs=2 we had this pcap:
https://thomas.glanzmann.de/tmp/tcp_auto_corking_on_patched_tcp_more_notlast.pcap.bz2
And here is the RTT TCP graph:
Wireshark > Statistics > TCP Stream Graph > Round Trip Time Graph
https://thomas.glanzmann.de/tmp/screenshot-mini-2014-02-10-22_04_30.png

with net.ipv4.tcp_min_tso_segs=8 we have this pcap:
https://thomas.glanzmann.de/tmp/tcp_auto_corking_on_patched_tcp_more_notlast_min_tso_segs_8.pcap.bz2
And here is the RTT TCP graph:
Wireshark > Statistics > TCP Stream Graph > Round Trip Time Graph

This gives us 0.0015 seconds RTT (1.5 ms)

Without TCP autocorking we had 0.0005 (0.5 ms).

https://thomas.glanzmann.de/tmp/screenshot-mini-2014-02-08-09:53:17.png

Cheers,
        Thomas
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