netdev - Re: [RFC PATCH 1/3] chelsio: cxgb: Remove ndo_poll

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Date:   Thu, 24 Dec 2020 14:31:37 +0100
From:   "Ahmed S. Darwish" <a.darwish@...utronix.de>
To:     Rahul Lakkireddy <rahul.lakkireddy@...lsio.com>,
        Rohit Maheshwari <rohitm@...lsio.com>,
        Vinay Kumar Yadav <vinay.yadav@...lsio.com>,
        Vishal Kulkarni <vishal@...lsio.com>, netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Sebastian A. Siewior" <bigeasy@...utronix.de>
Subject: Re: [RFC PATCH 1/3] chelsio: cxgb: Remove ndo_poll_controller()

[[ Actually adding Eric to Cc ]]

On Thu, Dec 24, 2020 at 02:11:46PM +0100, Ahmed S. Darwish wrote:
> Since commit ac3d9dd034e5 ("netpoll: make ndo_poll_controller()
> optional"), networking drivers which use NAPI for clearing their TX
> completions should not provide an ndo_poll_controller(). Netpoll simply
> triggers the necessary TX queues cleanup by synchronously calling the
> driver's NAPI poll handler -- with irqs off and a zero budget.
>
> Modify the cxgb's poll method to clear the TX queues upon zero budget.
> Per API requirements, make sure to never consume any RX packet in that
> case (budget=0), and thus also not to increment the budget upon return.
>
> Afterwards, remove ndo_poll_controller().
>
> Link: https://lkml.kernel.org/r/20180921222752.101307-1-edumazet@google.com
> Link: https://lkml.kernel.org/r/A782704A-DF97-4E85-B10A-D2268A67DFD7@fb.com
> References: 822d54b9c2c1 ("netpoll: Drop budget parameter from NAPI polling call hierarchy")
> Signed-off-by: Ahmed S. Darwish <a.darwish@...utronix.de>
> Cc: Eric Dumazet <edumazet@...gle.com>
> ---
>  drivers/net/ethernet/chelsio/cxgb/cxgb2.c | 14 --------------
>  drivers/net/ethernet/chelsio/cxgb/sge.c   |  9 ++++++++-
>  2 files changed, 8 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/net/ethernet/chelsio/cxgb/cxgb2.c b/drivers/net/ethernet/chelsio/cxgb/cxgb2.c
> index 0e4a0f413960..7b5a98330ef7 100644
> --- a/drivers/net/ethernet/chelsio/cxgb/cxgb2.c
> +++ b/drivers/net/ethernet/chelsio/cxgb/cxgb2.c
> @@ -878,17 +878,6 @@ static int t1_set_features(struct net_device *dev, netdev_features_t features)
>
>  	return 0;
>  }
> -#ifdef CONFIG_NET_POLL_CONTROLLER
> -static void t1_netpoll(struct net_device *dev)
> -{
> -	unsigned long flags;
> -	struct adapter *adapter = dev->ml_priv;
> -
> -	local_irq_save(flags);
> -	t1_interrupt(adapter->pdev->irq, adapter);
> -	local_irq_restore(flags);
> -}
> -#endif
>
>  /*
>   * Periodic accumulation of MAC statistics.  This is used only if the MAC
> @@ -973,9 +962,6 @@ static const struct net_device_ops cxgb_netdev_ops = {
>  	.ndo_set_mac_address	= t1_set_mac_addr,
>  	.ndo_fix_features	= t1_fix_features,
>  	.ndo_set_features	= t1_set_features,
> -#ifdef CONFIG_NET_POLL_CONTROLLER
> -	.ndo_poll_controller	= t1_netpoll,
> -#endif
>  };
>
>  static int init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
> diff --git a/drivers/net/ethernet/chelsio/cxgb/sge.c b/drivers/net/ethernet/chelsio/cxgb/sge.c
> index 2d9c2b5a690a..d6df1a87db0b 100644
> --- a/drivers/net/ethernet/chelsio/cxgb/sge.c
> +++ b/drivers/net/ethernet/chelsio/cxgb/sge.c
> @@ -1609,7 +1609,14 @@ static int process_pure_responses(struct adapter *adapter)
>  int t1_poll(struct napi_struct *napi, int budget)
>  {
>  	struct adapter *adapter = container_of(napi, struct adapter, napi);
> -	int work_done = process_responses(adapter, budget);
> +	int work_done = 0;
> +
> +	if (budget)
> +		work_done = process_responses(adapter, budget);
> +	else {
> +		/* budget=0 means: don't poll rx data */
> +		process_pure_responses(adapter);
> +	}
>
>  	if (likely(work_done < budget)) {
>  		napi_complete_done(napi, work_done);
> --
> 2.29.2
>