linux-kernel - Re: [PATCH 2/2] hv_netvsc: Use VF's tso_max

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Message-ID: <20250204215643.41d3f00f@hermes.local>
Date: Tue, 4 Feb 2025 21:56:43 -0800
From: Stephen Hemminger <stephen@...workplumber.org>
To: Shradha Gupta <shradhagupta@...ux.microsoft.com>
Cc: linux-hyperv@...r.kernel.org, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, "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>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
 <pabeni@...hat.com>, Long Li <longli@...rosoft.com>, Konstantin Taranov
 <kotaranov@...rosoft.com>, Souradeep Chakrabarti
 <schakrabarti@...ux.microsoft.com>, Erick Archer
 <erick.archer@...look.com>, Shradha Gupta <shradhagupta@...rosoft.com>
Subject: Re: [PATCH 2/2] hv_netvsc: Use VF's tso_max_size value when data
 path is VF

On Tue,  4 Feb 2025 20:21:55 -0800
Shradha Gupta <shradhagupta@...ux.microsoft.com> wrote:

> On Azure, increasing VF's TCP segment size to up-to GSO_MAX_SIZE
> is not possible without allowing the same for netvsc NIC
> (as the NICs are bonded together). For bonded NICs, the min of the max
> segment size of the members is propagated in the stack.
> 
> Therefore, we use netif_set_tso_max_size() to set max segment size
> to VF's segment size for netvsc too, when the data path is switched over
> to the VF
> Tested on azure env with Accelerated Networking enabled and disabled.
> 
> Signed-off-by: Shradha Gupta <shradhagupta@...ux.microsoft.com>
> Reviewed-by: Haiyang Zhang <haiyangz@...rosoft.com>

Since datapath can change at anytime (ie hot remove of VF).
How does TCP stack react to GSO max size changing underneath it.
Is it like a path MTU change where some packets are lost until
TCP retries and has to rediscover?