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

[Haiyang Zhang]

> -----Original Message-----
> From: Jakub Kicinski <kuba@xxxxxxxxxx>
> Sent: Wednesday, July 23, 2025 11:06 AM
> To: Jason Wang <jasowang@xxxxxxxxxx>
> Cc: Cindy Lu <lulu@xxxxxxxxxx>; KY Srinivasan <kys@xxxxxxxxxxxxx>; Haiyang
> Zhang <haiyangz@xxxxxxxxxxxxx>; Wei Liu <wei.liu@xxxxxxxxxx>; Dexuan Cui
> <decui@xxxxxxxxxxxxx>; Andrew Lunn <andrew+netdev@xxxxxxx>; David S.
> Miller <davem@xxxxxxxxxxxxx>; Eric Dumazet <edumazet@xxxxxxxxxx>; Paolo
> Abeni <pabeni@xxxxxxxxxx>; Simon Horman <horms@xxxxxxxxxx>; Michael Kelley
> <mhklinux@xxxxxxxxxxx>; Shradha Gupta <shradhagupta@xxxxxxxxxxxxxxxxxxx>;
> Kees Cook <kees@xxxxxxxxxx>; Stanislav Fomichev <sdf@xxxxxxxxxxx>;
> Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>; Alexander Lobakin
> <aleksander.lobakin@xxxxxxxxx>; Guillaume Nault <gnault@xxxxxxxxxx>; Joe
> Damato <jdamato@xxxxxxxxxx>; Ahmed Zaki <ahmed.zaki@xxxxxxxxx>; open
> list:Hyper-V/Azure CORE AND DRIVERS <linux-hyperv@xxxxxxxxxxxxxxx>; open
> list:NETWORKING DRIVERS <netdev@xxxxxxxxxxxxxxx>; open list <linux-
> kernel@xxxxxxxxxxxxxxx>
> 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
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> %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@xxxxxxxxxxxxxxxxxx>, in case he wants to
add more regarding the history.

Related patches:
author  Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>  2016-07-11 17:06:42 -0700
committer       David S. Miller <davem@xxxxxxxxxxxxx>   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@xxxxxxxxxxxxxxxxxx>  2017-08-01 19:58:55 -0700
committer       David S. Miller <davem@xxxxxxxxxxxxx>   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