netdev - Re: [PATCH net] mlx4: do not call napi

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Date:   Fri, 13 Jan 2017 15:07:31 -0800
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Erez Shitrit <erezsh@...lanox.com>,
        Eugenia Emantayev <eugenia@...lanox.com>,
        Tariq Toukan <tariqt@...lanox.com>
Subject: Re: [PATCH net] mlx4: do not call napi_schedule() without care

On Fri, Jan 13, 2017 at 8:39 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> From: Eric Dumazet <edumazet@...gle.com>
>
> Disable BH around the call to napi_schedule() to avoid following warning
>
> [   52.095499] NOHZ: local_softirq_pending 08
> [   52.421291] NOHZ: local_softirq_pending 08
> [   52.608313] NOHZ: local_softirq_pending 08
>
> Fixes: 8d59de8f7bb3 ("net/mlx4_en: Process all completions in RX rings after port goes up")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Erez Shitrit <erezsh@...lanox.com>
> Cc: Eugenia Emantayev <eugenia@...lanox.com>
> Cc: Tariq Toukan <tariqt@...lanox.com>
> ---
>  drivers/net/ethernet/mellanox/mlx4/en_netdev.c |    5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/mellanox/mlx4/en_netdev.c b/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
> index 4910d9af19335d4b97d39760c163b41eecc26242..761f8b12399cab245abccc0f7d7f84fde742c14d 100644
> --- a/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
> +++ b/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
> @@ -1748,8 +1748,11 @@ int mlx4_en_start_port(struct net_device *dev)
>         /* Process all completions if exist to prevent
>          * the queues freezing if they are full
>          */
> -       for (i = 0; i < priv->rx_ring_num; i++)
> +       for (i = 0; i < priv->rx_ring_num; i++) {
> +               local_bh_disable();
>                 napi_schedule(&priv->rx_cq[i]->napi);
> +               local_bh_enable();
> +       }

Couldn't you save yourself a ton of trouble by wrapping the loop
inside of the local_bh_disable/enable instead of wrapping them up
inside the loop?  It just seems like it might be more efficient to
schedule them and then process them as a block instead of doing it one
at a time.

- Alex