netdev - Re: [PATCH net 10/11] sfc-falcon: remove ndo_poll

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Date:   Fri, 28 Sep 2018 08:30:18 +0100
From:   Bert Kenward <bkenward@...arflare.com>
To:     Eric Dumazet <edumazet@...gle.com>,
        "David S . Miller" <davem@...emloft.net>
CC:     netdev <netdev@...r.kernel.org>,
        Michael Chan <michael.chan@...adcom.com>,
        Aviad Krawczyk <aviad.krawczyk@...wei.com>,
        Song Liu <songliubraving@...com>,
        Douglas Miller <dougmill@...ux.vnet.ibm.com>,
        Yisen Zhuang <yisen.zhuang@...wei.com>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Harish Patil <harish.patil@...ium.com>,
        Manish Chopra <manish.chopra@...ium.com>,
        Netanel Belgazal <netanel@...zon.com>,
        "Solarflare linux maintainers" <linux-net-drivers@...arflare.com>,
        Thomas Falcon <tlfalcon@...ux.vnet.ibm.com>,
        Edward Cree <ecree@...arflare.com>
Subject: Re: [PATCH net 10/11] sfc-falcon: remove ndo_poll_controller

On 27/09/18 17:32, Eric Dumazet wrote:
> As diagnosed by Song Liu, ndo_poll_controller() can
> be very dangerous on loaded hosts, since the cpu
> calling ndo_poll_controller() might steal all NAPI
> contexts (for all RX/TX queues of the NIC). This capture
> can last for unlimited amount of time, since one
> cpu is generally not able to drain all the queues under load.
> 
> sfc-falcon uses NAPI for TX completions, so we better let core
> networking stack call the napi->poll() to avoid the capture.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Solarflare linux maintainers <linux-net-drivers@...arflare.com>
> Cc: Edward Cree <ecree@...arflare.com>
> Cc: Bert Kenward <bkenward@...arflare.com>

Acked-By: Bert Kenward <bkenward@...arflare.com>

> ---
>  drivers/net/ethernet/sfc/falcon/efx.c | 26 --------------------------
>  1 file changed, 26 deletions(-)
> 
> diff --git a/drivers/net/ethernet/sfc/falcon/efx.c b/drivers/net/ethernet/sfc/falcon/efx.c
> index dd5530a4f8c8936868aed7171bd9481f93730d76..03e2455c502eacd9a4fd5c7fd320a9edcf265f77 100644
> --- a/drivers/net/ethernet/sfc/falcon/efx.c
> +++ b/drivers/net/ethernet/sfc/falcon/efx.c
> @@ -2052,29 +2052,6 @@ static void ef4_fini_napi(struct ef4_nic *efx)
>  		ef4_fini_napi_channel(channel);
>  }
>  
> -/**************************************************************************
> - *
> - * Kernel netpoll interface
> - *
> - *************************************************************************/
> -
> -#ifdef CONFIG_NET_POLL_CONTROLLER
> -
> -/* Although in the common case interrupts will be disabled, this is not
> - * guaranteed. However, all our work happens inside the NAPI callback,
> - * so no locking is required.
> - */
> -static void ef4_netpoll(struct net_device *net_dev)
> -{
> -	struct ef4_nic *efx = netdev_priv(net_dev);
> -	struct ef4_channel *channel;
> -
> -	ef4_for_each_channel(channel, efx)
> -		ef4_schedule_channel(channel);
> -}
> -
> -#endif
> -
>  /**************************************************************************
>   *
>   * Kernel net device interface
> @@ -2250,9 +2227,6 @@ static const struct net_device_ops ef4_netdev_ops = {
>  	.ndo_set_mac_address	= ef4_set_mac_address,
>  	.ndo_set_rx_mode	= ef4_set_rx_mode,
>  	.ndo_set_features	= ef4_set_features,
> -#ifdef CONFIG_NET_POLL_CONTROLLER
> -	.ndo_poll_controller = ef4_netpoll,
> -#endif
>  	.ndo_setup_tc		= ef4_setup_tc,
>  #ifdef CONFIG_RFS_ACCEL
>  	.ndo_rx_flow_steer	= ef4_filter_rfs,
>