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

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Date:   Fri, 24 Nov 2017 10:52:44 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     David Ahern <dsahern@...il.com>,
        Solio Sarabia <solio.sarabia@...el.com>,
        netdev@...r.kernel.org, davem@...eloft.net,
        stephen@...workplumber.org
Cc:     kys@...rosoft.com, shiny.sebastian@...el.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net-sysfs: export gso_max_size attribute

On Fri, 2017-11-24 at 11:43 -0700, David Ahern wrote:
> On 11/24/17 11:32 AM, Eric Dumazet wrote:
> > On Fri, 2017-11-24 at 10:14 -0700, David Ahern wrote:
> > > On 11/22/17 5:30 PM, Solio Sarabia 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>
> > > > ---
> > > 
> > > This should be added to rtnetlink rather than sysfs.
> > 
> > This is already exposed by rtnetlink [1]
> 
> It currently is read-only. This patch wants to control setting it.
> 
> > 
> > Please lets not add yet another net-sysfs knob.
> 
> Which is my main point - no more sysfs files.
> 

I was not objecting to your point, sorry if this was not obvious.

I usually hit reply on the latest email, not the first one in the
thread.

Proper support for changing these attributes is more complex than that
trivial change. Bonding and team devices, and tunnels comes to mind.