netdev - Re: [PATCH v2 net-next 14/14] mlx5: support BIG TCP packets

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Message-ID: <c9f5c261-c263-a6b4-7e00-17dfefd36a7a@kernel.org>
Date:   Thu, 3 Mar 2022 21:42:59 -0700
From:   David Ahern <dsahern@...nel.org>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Coco Li <lixiaoyan@...gle.com>,
        Alexander Duyck <alexanderduyck@...com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Leon Romanovsky <leon@...nel.org>
Subject: Re: [PATCH v2 net-next 14/14] mlx5: support BIG TCP packets

On 3/3/22 11:16 AM, Eric Dumazet wrote:
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> index b2ed2f6d4a9208aebfd17fd0c503cd1e37c39ee1..1e51ce1d74486392a26568852c5068fe9047296d 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> @@ -4910,6 +4910,7 @@ static void mlx5e_build_nic_netdev(struct net_device *netdev)
>  
>  	netdev->priv_flags       |= IFF_UNICAST_FLT;
>  
> +	netif_set_tso_ipv6_max_size(netdev, 512 * 1024);


How does the ConnectX hardware handle fairness for such large packet
sizes? For 1500 MTU this means a single large TSO can cause the H/W to
generate 349 MTU sized packets. Even a 4k MTU means 128 packets. This
has an effect on the rate of packets hitting the next hop switch for
example.