netdev - Re: [PATCH RESEND] netvsc: transfer lower device max tso size

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Message-ID: <20250721181807.752af6a4@kernel.org>
Date: Mon, 21 Jul 2025 18:18:07 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Jason Wang <jasowang@...hat.com>
Cc: Cindy Lu <lulu@...hat.com>, "K. Y. Srinivasan" <kys@...rosoft.com>,
 Haiyang Zhang <haiyangz@...rosoft.com>, Wei Liu <wei.liu@...nel.org>,
 Dexuan Cui <decui@...rosoft.com>, Andrew Lunn <andrew+netdev@...n.ch>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Simon Horman
 <horms@...nel.org>, Michael Kelley <mhklinux@...look.com>, Shradha Gupta
 <shradhagupta@...ux.microsoft.com>, Kees Cook <kees@...nel.org>, Stanislav
 Fomichev <sdf@...ichev.me>, Kuniyuki Iwashima <kuniyu@...gle.com>,
 Alexander Lobakin <aleksander.lobakin@...el.com>, Guillaume Nault
 <gnault@...hat.com>, Joe Damato <jdamato@...tly.com>, Ahmed Zaki
 <ahmed.zaki@...el.com>, "open list:Hyper-V/Azure CORE AND DRIVERS"
 <linux-hyperv@...r.kernel.org>, "open list:NETWORKING DRIVERS"
 <netdev@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RESEND] netvsc: transfer lower device max tso size

On Tue, 22 Jul 2025 09:04:20 +0800 Jason Wang wrote:
> On Tue, Jul 22, 2025 at 7:28 AM Jakub Kicinski <kuba@...nel.org> wrote:
> > On Fri, 18 Jul 2025 14:17:55 +0800 Cindy Lu wrote:  
> > > Subject: [PATCH RESEND] netvsc: transfer lower device max tso size  
> >
> > You say RESEND but I don't see a link to previous posting anywhere.

Someone should respond to this part, please.

> > I'd rather we didn't extend the magic behavior of hyperv/netvsc any
> > further.  
> 
> Are you referring to the netdev coupling model of the VF acceleration?

Yes, it tries to apply whole bunch of policy automatically in 
the kernel.

> > We have enough problems with it.
> 
> But this fixes a real problem, otherwise nested VM performance will be
> broken due to the GSO software segmentation.

Perhaps, possibly, a migration plan can be devised, away from the
netvsc model, so we don't have to deal with nuggets of joy like:
https://lore.kernel.org/all/1752870014-28909-1-git-send-email-haiyangz@linux.microsoft.com/