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

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Date:	Mon, 02 Feb 2015 10:52:16 -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 Mon, 2015-02-02 at 11:27 +0100, Michal Kazior wrote:

> While testing I've had my internal GRO patch for ath10k and no stretch
> ack patches.

Thanks for the data, I took a look at it.

I am afraid this GRO patch might be the problem.

It seems to break ACK clocking badly (linux stack has a somewhat buggy
tcp_tso_should_defer(), which relies on ACK being received smoothly, as
no timer is setup to split the TSO packet.)

I am seeing huge delays on ACK packets and bursts like that :

05:01:53.413038 IP 192.168.1.2.5001 > 192.168.1.3.49669: Flags [.], ack 76745, win 4435, options [nop,nop,TS val 4294758508 ecr 4294757300], length 0
05:01:53.413407 IP 192.168.1.2.5001 > 192.168.1.3.49669: Flags [.], ack 79641, win 4435, options [nop,nop,TS val 4294758508 ecr 4294757301], length 0
05:01:53.413969 IP 192.168.1.2.5001 > 192.168.1.3.49669: Flags [.], ack 92673, win 4435, options [nop,nop,TS val 4294758510 ecr 4294757302], length 0
05:01:53.413990 IP 192.168.1.2.5001 > 192.168.1.3.49669: Flags [.], ack 97017, win 4435, options [nop,nop,TS val 4294758510 ecr 4294757302], length 0
05:01:53.414011 IP 192.168.1.2.5001 > 192.168.1.3.49669: Flags [.], ack 110049, win 4435, options [nop,nop,TS val 4294758510 ecr 4294757302], length 0
...
05:01:53.422663 IP 192.168.1.2.5001 > 192.168.1.3.49669: Flags [.], ack 189689, win 4435, options [nop,nop,TS val 4294758519 ecr 4294757310], length 0
05:01:53.424354 IP 192.168.1.2.5001 > 192.168.1.3.49669: Flags [.], ack 198377, win 4435, options [nop,nop,TS val 4294758520 ecr 4294757311], length 0
05:01:53.424400 IP 192.168.1.2.5001 > 192.168.1.3.49669: Flags [.], ack 202721, win 4435, options [nop,nop,TS val 4294758520 ecr 4294757313], length 0
05:01:53.424409 IP 192.168.1.2.5001 > 192.168.1.3.49669: Flags [.], ack 205617, win 4435, options [nop,nop,TS val 4294758520 ecr 4294757313], length 0
...
05:01:53.450248 IP 192.168.1.2.5001 > 192.168.1.3.49669: Flags [.], ack 419921, win 4435, options [nop,nop,TS val 4294758547 ecr 4294757337], length 0
05:01:53.450266 IP 192.168.1.2.5001 > 192.168.1.3.49669: Flags [.], ack 427161, win 4435, options [nop,nop,TS val 4294758547 ecr 4294757340], length 0
05:01:53.450289 IP 192.168.1.2.5001 > 192.168.1.3.49669: Flags [.], ack 431505, win 4435, options [nop,nop,TS val 4294758547 ecr 4294757340], length 0

Could you make again your experiments using upstream kernel (David
Miller net tree) ?

You also could post the GRO patch so that we can comment on it.

Thanks


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