netdev - Re: [PATCH v4 net-next 07/13] mlx4: use order-0 pages for RX

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Date:   Thu, 9 Mar 2017 15:55:48 +0200
From:   Tariq Toukan <tariqt@...lanox.com>
To:     Eric Dumazet <edumazet@...gle.com>,
        "David S . Miller" <davem@...emloft.net>
CC:     netdev <netdev@...r.kernel.org>,
        Tariq Toukan <tariqt@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH v4 net-next 07/13] mlx4: use order-0 pages for RX



On 08/03/2017 6:17 PM, Eric Dumazet wrote:
> Use of order-3 pages is problematic in some cases.
>
> This patch might add three kinds of regression :
>
> 1) a CPU performance regression, but we will add later page
> recycling and performance should be back.
>
> 2) TCP receiver could grow its receive window slightly slower,
>    because skb->len/skb->truesize ratio will decrease.
>    This is mostly ok, we prefer being conservative to not risk OOM,
>    and eventually tune TCP better in the future.
>    This is consistent with other drivers using 2048 per ethernet frame.
>
> 3) Because we allocate one page per RX slot, we consume more
>    memory for the ring buffers. XDP already had this constraint anyway.
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> ---
>  drivers/net/ethernet/mellanox/mlx4/en_rx.c   | 72 +++++++++++++---------------
>  drivers/net/ethernet/mellanox/mlx4/mlx4_en.h |  5 --
>  2 files changed, 33 insertions(+), 44 deletions(-)
>
Acked-by: Tariq Toukan <tariqt@...lanox.com>

Thanks.