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

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Date:	Fri, 6 Feb 2015 15:08:19 +0100
From:	Michal Kazior <michal.kazior@...to.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Neal Cardwell <ncardwell@...gle.com>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	Eyal Perry <eyalpe@....mellanox.co.il>
Subject: Re: Throughput regression with `tcp: refine TSO autosizing`

On 6 February 2015 at 14:40, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Fri, 2015-02-06 at 10:42 +0100, Michal Kazior wrote:
>
>> The above brings back previous behaviour, i.e. I can get 600mbps TCP
>> on 5 flows again. Single flow is still (as it was before TSO
>> autosizing) limited to roughly ~280mbps.
>>
>> I never really bothered before to understand why I need to push a few
>> flows through ath10k to max it out, i.e. if I run a single UDP flow I
>> get ~300mbps while with, e.g. 5 I get 670mbps easily.
>>
>
> For single UDP flow, tweaking /proc/sys/net/core/wmem_default might be
> enough : UDP has no callback from TX completion to feed following frames
> (No write queue like TCP)
>
> # cat /proc/sys/net/core/wmem_default
> 212992
> # ethtool -C eth1 tx-usecs 1024 tx-frames 120
> # ./netperf -H remote -t UDP_STREAM -- -m 1450
> Socket  Message  Elapsed      Messages
> Size    Size     Time         Okay Errors   Throughput
> bytes   bytes    secs            #      #   10^6bits/sec
>
> 212992    1450   10.00      697705      0     809.27
> 212992           10.00      673412            781.09
>
> # echo 800000 >/proc/sys/net/core/wmem_default
> # ./netperf -H remote -t UDP_STREAM -- -m 1450
> Socket  Message  Elapsed      Messages
> Size    Size     Time         Okay Errors   Throughput
> bytes   bytes    secs            #      #   10^6bits/sec
>
> 800000    1450   10.00     7329221      0    8501.84
> 212992           10.00     7284051           8449.44

Hmm.. I confirm it works. However the value at which I get full rate
on a single flow is more than 2048K. Also using non-default
wmem_default seems to introduce packet loss as per iperf reports at
the receiver. I suppose this is kind of expected but on the other hand
wmem_default=262992 and 5 flows of UDP max the device out with 0
packet loss.


Michał
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