netdev - Re: [PATCH] net-sysfs: export gso_max

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Date:   Thu, 23 Nov 2017 21:18:37 -0800
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Solio Sarabia <solio.sarabia@...el.com>
Cc:     netdev@...r.kernel.org, davem@...eloft.net, kys@...rosoft.com,
        shiny.sebastian@...el.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net-sysfs: export gso_max_size attribute

On Wed, 22 Nov 2017 16:30:41 -0800
Solio Sarabia <solio.sarabia@...el.com> wrote:

> The netdevice gso_max_size is exposed to allow users fine-control on
> systems with multiple NICs with different GSO buffer sizes, and where
> the virtual devices like bridge and veth, need to be aware of the GSO
> size of the underlying devices.
> 
> In a virtualized environment, setting the right GSO sizes for physical
> and virtual devices makes all TSO work to be on physical NIC, improving
> throughput and reducing CPU util. If virtual devices send buffers
> greater than what NIC supports, it forces host to do TSO for buffers
> exceeding the limit, increasing CPU utilization in host.
> 
> Suggested-by: Shiny Sebastian <shiny.sebastian@...el.com>
> Signed-off-by: Solio Sarabia <solio.sarabia@...el.com>
> ---
> In one test scenario with Hyper-V host, Ubuntu 16.04 VM, with Docker
> inside VM, and NTttcp sending 40 Gbps from one container, setting the
> right gso_max_size values for all network devices in the chain, reduces
> CPU overhead about 3x (for the sender), since all TSO work is done by
> physical NIC.
> 
>  net/core/net-sysfs.c | 30 ++++++++++++++++++++++++++++++
>  1 file changed, 30 insertions(+)


You probably should expose gso_max_segs as well.