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

On 3 February 2015 at 02:18, Eric Dumazet [off-list ref] wrote:

On Mon, 2015-02-02 at 10:52 -0800, Eric Dumazet wrote:

quoted

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