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

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Message-ID:
 <SJ2PR21MB40138F71138A809C3A2D903BCA5FA@SJ2PR21MB4013.namprd21.prod.outlook.com>
Date: Wed, 23 Jul 2025 20:18:03 +0000
From: Haiyang Zhang <haiyangz@...rosoft.com>
To: Jakub Kicinski <kuba@...nel.org>, Jason Wang <jasowang@...hat.com>,
	Stephen Hemminger <stephen@...workplumber.org>
CC: Cindy Lu <lulu@...hat.com>, KY Srinivasan <kys@...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



> -----Original Message-----
> From: Jakub Kicinski <kuba@...nel.org>
> Sent: Wednesday, July 23, 2025 11:06 AM
> To: Jason Wang <jasowang@...hat.com>
> Cc: Cindy Lu <lulu@...hat.com>; KY 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: [EXTERNAL] Re: [PATCH RESEND] netvsc: transfer lower device max
> tso size
>
> On Wed, 23 Jul 2025 14:00:47 +0800 Jason Wang wrote:
> > > > 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.ker/
> nel.org%2Fall%2F1752870014-28909-1-git-send-email-
> haiyangz%40linux.microsoft.com%2F&data=05%7C02%7Chaiyangz%40microsoft.com%
> 7C27aa73c4b6e9446c7f6508ddc9fa6053%7C72f988bf86f141af91ab2d7cd011db47%7C1%
> 7C0%7C638888799449774753%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsI
> lYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C
> %7C%7C&sdata=HYX4dDie8QlEepzwPiiI3eYASe7WN5o%2BWTXmMGoyFOM%3D&reserved=0
> >
> > Btw, if I understand this correctly. This is for future development so
> > it's not a blocker for this patch?
>
> Not a blocker, I'm just giving an example of the netvsc auto-weirdness
> being a source of tech debt and bugs. Commit d7501e076d859d is another
> recent one off the top of my head. IIUC systemd-networkd is broadly
> deployed now. It'd be great if there was some migration plan for moving
> this sort of VM auto-bonding to user space (with the use of the common
> bonding driver, not each hypervisor rolling its own).

Actually, we had used the common bonding driver 9 years ago. But it's
replaced by this kernel/netvsc based "transparent" bonding mode. See
the patches listed below.

The user mode bonding scripts were unstable, and difficult to deliver
& update for various distros. So Stephen developed the new "transparent"
bonding mode, which greatly improves the situation.
@Stephen Hemminger <stephen@...workplumber.org>, in case he wants to
add more regarding the history.

Related patches:
author  Haiyang Zhang <haiyangz@...rosoft.com>  2016-07-11 17:06:42 -0700
committer       David S. Miller <davem@...emloft.net>   2016-07-12 10:41:53 -0700
commit  178cd55f086629cf0bad9c66c793a7e2bcc3abb6 (patch)
tools: hv: Add a script to help bonding synthetic and VF NICs

author  stephen hemminger <stephen@...workplumber.org>  2017-08-01 19:58:55 -0700
committer       David S. Miller <davem@...emloft.net>   2017-08-02 16:55:33 -0700
commit  12aa7469d101e139b3728e540884bc7d72dca70a (patch)
netvsc: remove bonding setup script
No longer needed, now all managed by transparent VF logic.

Thanks,
- Haiyang