netdev - Re: [PATCH V2 net-next] net/mlx4_en: avoid one cache line miss to ring doorbell

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Message-ID: <c677b3d3-62d4-7e1c-24a0-a099ce28f12a@gmail.com>
Date:   Sun, 3 Oct 2021 11:05:54 +0300
From:   Tariq Toukan <ttoukan.linux@...il.com>
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>,
        Tariq Toukan <tariqt@...dia.com>
Subject: Re: [PATCH V2 net-next] net/mlx4_en: avoid one cache line miss to
 ring doorbell



On 10/1/2021 3:52 AM, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> 
> This patch caches doorbell address directly in struct mlx4_en_tx_ring.
> 
> This removes the need to bring in cpu caches whole struct mlx4_uar
> in fast path.
> 
> Note that mlx4_uar is not guaranteed to be on a local node,
> because mlx4_bf_alloc() uses a single free list (priv->bf_list)
> regardless of its node parameter.
> 
> This kind of change does matter in presence of light/moderate traffic.
> In high stress, this read-only line would be kept hot in caches.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Tariq Toukan <tariqt@...dia.com>
> ---
> V2: added __iomem attribute to remove sparse errors (Jakub)
> 
>   drivers/net/ethernet/mellanox/mlx4/en_tx.c   | 4 ++--
>   drivers/net/ethernet/mellanox/mlx4/mlx4_en.h | 1 +
>   2 files changed, 3 insertions(+), 2 deletions(-)
> 


Thanks for your patch.
Reviewed-by: Tariq Toukan <tariqt@...dia.com>