netdev - Re: [PATCH net] net: change maximum number of UDP segments to 128

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Message-ID: <20240409163116.0b1525c5@kernel.org>
Date: Tue, 9 Apr 2024 16:31:16 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Yuri Benditovich <yuri.benditovich@...nix.com>
Cc: Willem de Bruijn <willemdebruijn.kernel@...il.com>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni
 <pabeni@...hat.com>, Shuah Khan <shuah@...nel.org>, Jason Wang
 <jasowang@...hat.com>, yan@...nix.com, andrew@...nix.com,
 "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net] net: change maximum number of UDP segments to 128

CC: netdev@

On Sat,  6 Apr 2024 21:50:29 +0300 Yuri Benditovich wrote:
> Fixes: fc8b2a619469378 ("net: more strict VIRTIO_NET_HDR_GSO_UDP_L4 validation")
> 

Fixes: line goes right above your sign-off, no empty lines in between
them.

> The mentioned above commit adds check of potential number
> of UDP segments vs UDP_MAX_SEGMENTS in linux/virtio_net.h.
> After this change certification test of USO guest-to-guest
> transmit on Windows driver for virtio-net device fails,
> for example with packet size of ~64K and mss of 536 bytes.
> In general the USO should not be more restrictive than TSO.
> Indeed, in case of unreasonably small mss a lot of segments
> can cause queue overflow and packet loss on the destination.
> Limit of 128 segments is good for any practical purpose,
> with minimal meaningful mss of 536 the maximal UDP packet will
> be divided to ~120 segments.
> 
> Signed-off-by: Yuri Benditovich <yuri.benditovich@...nix.com>