netdev - Re: TCP and BBR: reproducibly low cwnd and bandwidth

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Date:   Sun, 18 Feb 2018 14:24:09 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Oleksandr Natalenko <oleksandr@...alenko.name>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        Neal Cardwell <ncardwell@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>,
        Yuchung Cheng <ycheng@...gle.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>,
        Jerry Chu <hkchu@...gle.com>, Dave Taht <dave.taht@...il.com>
Subject: Re: TCP and BBR: reproducibly low cwnd and bandwidth

On Sun, 2018-02-18 at 22:49 +0100, Oleksandr Natalenko wrote:
> Hi.
> 
> On neděle 18. února 2018 22:04:27 CET Eric Dumazet wrote:
> > I was able to take a look today, and I believe this is the time to
> > switch TCP to GSO being always on.
> > 
> > As a bonus, we get speed boost for cubic as well.
> > 
> > Todays high BDP and recent TCP improvements (rtx queue as rb-tree, sack
> > coalescing, TCP pacing...) all were developed/tested/maintained with
> > GSO/TSO being the norm.
> > 
> > Can you please test the following patch ?
> 
> Yes, results below:
> 
> BBR+fq:
> sg on:  6.02 Gbits/sec
> sg off: 1.33 Gbits/sec
> 
> BBR+pfifo_fast:
> sg on:  4.13 Gbits/sec
> sg off: 1.34 Gbits/sec
> 
> BBR+fq_codel:
> sg on:  4.16 Gbits/sec
> sg off: 1.35 Gbits/sec
> 
> Reno+fq:
> sg on:  6.44 Gbits/sec
> sg off: 1.39 Gbits/sec
> 
> Reno+pfifo_fast:
> sg on:  6.36 Gbits/sec
> sg off: 1.39 Gbits/sec
> 
> Reno+fq_codel:
> sg on:  6.41 Gbits/sec
> sg off: 1.38 Gbits/sec
> 
> While BBR still suffers when fq is not used, disabling sg doesn't bring 
> drastic throughput drop anymore. So, looks good to me, eh?
> 

Indeed :)

Here are my results on 40Gbit link (mlx4) :

BBR+fq:
sg on:  26 Gbits/sec
sg off: 15.7 Gbits/sec   (was 2.3 Gbit before patch)

BBR+pfifo_fast:
sg on:  24.2 Gbits/sec
sg off: 14.9 Gbits/sec  (was 0.66 Gbit before patch !!! )

BBR+fq_codel:
sg on:  24.4 Gbits/sec
sg off: 15 Gbits/sec  (was 0.66 Gbit before patch !!! )

Reno+fq:
sg on:  20 Gbits/sec
sg off: 15.7 Gbits/sec  (was 6 Gbit)

Reno+pfifo_fast:
sg on:  25.7 Gbits/sec
sg off: 15.5 Gbits/sec  (was 7 Gbit)

Reno+fq_codel:
sg on:  25.8 Gbits/sec
sg off: 16 Gbits/sec    (was 7 Gbit)

Definitely worth it ;)

Thanks !