netdev - Re: [PATCH RFC 11/11] net/mlx5e: XDP TX xmit more

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Date:   Wed, 7 Sep 2016 20:22:34 +0200
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Saeed Mahameed <saeedm@....mellanox.co.il>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        iovisor-dev <iovisor-dev@...ts.iovisor.org>,
        Linux Netdev List <netdev@...r.kernel.org>,
        Tariq Toukan <tariqt@...lanox.com>,
        Brenden Blanco <bblanco@...mgrid.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Tom Herbert <tom@...bertland.com>,
        Martin KaFai Lau <kafai@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jamal Hadi Salim <jhs@...atatu.com>, brouer@...hat.com
Subject: Re: [PATCH RFC 11/11] net/mlx5e: XDP TX xmit more


On Wed, 7 Sep 2016 19:57:19 +0300 Saeed Mahameed <saeedm@....mellanox.co.il> wrote:
> On Wed, Sep 7, 2016 at 6:32 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > On Wed, 2016-09-07 at 18:08 +0300, Saeed Mahameed wrote:  
> >> On Wed, Sep 7, 2016 at 5:41 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:  
> >> > On Wed, 2016-09-07 at 15:42 +0300, Saeed Mahameed wrote:  
[...]
> >
> > Only if a qdisc is present and pressure is high enough.
> >
> > But in a forwarding setup, we likely receive at a lower rate than the
> > NIC can transmit.

Yes, I can confirm this happens in my experiments.

> >  
> 
> Jesper has a similar Idea to make the qdisc think it is under
> pressure, when the device TX ring is idle most of the time, i think
> his idea can come in handy here. I am not fully involved in the
> details, maybe he can elaborate more.
> 
> But if it works, it will be transparent to napi, and xmit more will
> happen by design.

Yes. I have some ideas around getting more bulking going from the qdisc
layer, by having the drivers provide some feedback to the qdisc layer
indicating xmit_more should be possible.  This will be a topic at the
Network Performance Workshop[1] at NetDev 1.2, I have will hopefully
challenge people to come up with a good solution ;-)

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer

[1] http://netdevconf.org/1.2/session.html?jesper-performance-workshop