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

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Date:	Tue, 3 Feb 2015 12:50:59 +0100
From:	Michal Kazior <michal.kazior@...to.com>
To:	Eric Dumazet <eric.dumazet@...il.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 3 February 2015 at 02:18, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Mon, 2015-02-02 at 10:52 -0800, Eric Dumazet wrote:
>
>> 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.)
>
> Following patch might help the TSO split defer logic.
>
> It would avoid setting the TSO defer 'pseudo timer' twice, if/when TCP
> Small Queue logic prevented the xmit at the expiration of first 'timer'.
>
> This patch clears the tso_deferred variable only if we could really
> send something.
>
> Please try it, thanks !
[..patch..]

I've done a second round of tests. I've added the A-MSDU count
parameter I've mentioned in my other email into the mix.

 net - net/master (includes stretch ack patches)
 net-tso - net/master + your TSO defer patch
 net-gro - net/master + my ath10k GRO patch
 net-gro-tso - net/master + duh

Here's the best of amsdu count 1 and 3:

 ; for (i in */output.txt) { echo $i; for (j in (1 3)) { cat $i | awk
'x && /Mbits/ {y=$0}; x && y && !/Mbits/ {print y; x=0; y=""}; /set
amsdu cnt to '$j'/{x=1}' | awk '{ if (x < $(NF-1)) {x=$(NF-1)} }
END{print "A-MSDU limit='$j', " x " Mbits/sec"}' } }
 net-gro-tso/output.txt
 A-MSDU limit=1, 436 Mbits/sec
 A-MSDU limit=3, 284 Mbits/sec
 net-gro/output.txt
 A-MSDU limit=1, 444 Mbits/sec
 A-MSDU limit=3, 283 Mbits/sec
 net-tso/output.txt
 A-MSDU limit=1, 376 Mbits/sec
 A-MSDU limit=3, 251 Mbits/sec
 net/output.txt
 A-MSDU limit=1, 387 Mbits/sec
 A-MSDU limit=3, 260 Mbits/sec

IOW:
 - stretch acks / TSO defer don't seem to help much (when compared to
throughput results from yesterday)
 - GRO helps
 - disabling A-MSDU on sender helps
 - net/master+GRO still doesn't reach the performance from before the
regression (~600mbps w/ GRO)

You can grab logs and dumps here: http://www.filedropper.com/test2tar


Michał
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