netdev - Re: Throughput regression with `tcp: refine TSO autosizing`

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Message-ID: <1422628835.21689.95.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Fri, 30 Jan 2015 06:40:35 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Michal Kazior <michal.kazior@...to.com>
Cc:	linux-wireless <linux-wireless@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	eyalpe@....mellanox.co.il
Subject: Re: Throughput regression with `tcp: refine TSO autosizing`

On Fri, 2015-01-30 at 14:39 +0100, Michal Kazior wrote:

> I've briefly tried playing with this knob to no avail unfortunately. I
> tried 256K, 1M - it didn't improve TCP performance. When I tried to
> make it smaller (e.g. 16K) the traffic dropped even more so it does
> have an effect. It seems there's some other limiting factor in this
> case.

Interesting.

Could you take some tcpdump/pcap with various tcp_limit_output_bytes
values ?

echo 131072 >/proc/sys/net/ipv4/tcp_limit_output_bytes
tcpdump -p -i wlanX -s 128 -c 20000 -w 128k.pcap

echo 262144 >/proc/sys/net/ipv4/tcp_limit_output_bytes
tcpdump -p -i wlanX -s 128 -c 20000 -w 256k.pcap

...

Thanks !


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