Subject: Re: [PATCH net 2/2] igc: Modify the tx-usecs coalesce setting

From: Simon Horman <[email-masked]>
Date: Sun, 30 Jul 2023 17:54:09 +0200

On Fri, Jul 28, 2023 at 10:09:54AM -0700, Tony Nguyen wrote:
> From: Muhammad Husaini Zulkifli <[email-masked]>
> 
> This patch enables users to modify the tx-usecs parameter.
> The rx-usecs value will adhere to the same value as tx-usecs
> if the queue pair setting is enabled.
> 
> How to test:
> User can set the coalesce value using ethtool command.
> 
> Example command:
> Set: ethtool -C <interface>
> 
> Previous output:
> 
> root@P12DYHUSAINI:~# ethtool -C enp170s0 tx-usecs 10
> netlink error: Invalid argument
> 
> New output:
> 
> root@P12DYHUSAINI:~# ethtool -C enp170s0 tx-usecs 10
> rx-usecs: 10
> rx-frames: n/a
> rx-usecs-irq: n/a
> rx-frames-irq: n/a
> 
> tx-usecs: 10
> tx-frames: n/a
> tx-usecs-irq: n/a
> tx-frames-irq: n/a
> 
> Fixes: 8c5ad0dae93c ("igc: Add ethtool support")
> Signed-off-by: Muhammad Husaini Zulkifli <[email-masked]>
> Tested-by: Naama Meir <[email-masked]>
> Signed-off-by: Tony Nguyen <[email-masked]>
> ---
>  drivers/net/ethernet/intel/igc/igc_ethtool.c | 33 ++++++++++++++++++--
>  1 file changed, 30 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/igc/igc_ethtool.c b/drivers/net/ethernet/intel/igc/igc_ethtool.c
> index 62d925b26f2c..1cf7131a82c5 100644
> --- a/drivers/net/ethernet/intel/igc/igc_ethtool.c
> +++ b/drivers/net/ethernet/intel/igc/igc_ethtool.c
> @@ -914,6 +914,34 @@ static int igc_ethtool_set_coalesce(struct net_device *netdev,
>  			adapter->flags &= ~IGC_FLAG_DMAC;
>  	}
>  
> +	if (adapter->flags & IGC_FLAG_QUEUE_PAIRS) {
> +		u32 old_tx_itr, old_rx_itr;
> +
> +		/* This is to get back the original value before byte shifting */
> +		old_tx_itr = (adapter->tx_itr_setting <= 3) ?
> +			      adapter->tx_itr_setting : adapter->tx_itr_setting >> 2;
> +
> +		old_rx_itr = (adapter->rx_itr_setting <= 3) ?
> +			      adapter->rx_itr_setting : adapter->rx_itr_setting >> 2;
> +
> +		if (old_tx_itr != ec->tx_coalesce_usecs) {
> +			if (ec->tx_coalesce_usecs && ec->tx_coalesce_usecs <= 3)
> +				adapter->tx_itr_setting = ec->tx_coalesce_usecs;
> +			else
> +				adapter->tx_itr_setting = ec->tx_coalesce_usecs << 2;
> +
> +			adapter->rx_itr_setting = adapter->tx_itr_setting;
> +		} else if (old_rx_itr != ec->rx_coalesce_usecs) {
> +			if (ec->rx_coalesce_usecs && ec->rx_coalesce_usecs <= 3)
> +				adapter->rx_itr_setting = ec->rx_coalesce_usecs;
> +			else
> +				adapter->rx_itr_setting = ec->rx_coalesce_usecs << 2;
> +
> +			adapter->tx_itr_setting = adapter->rx_itr_setting;
> +		}
> +		goto program_itr;

This goto seems fairly gratuitous to me.
Couldn't the code be refactored to avoid it,
f.e. by moving ~10 lines below into an else clause?

My main objection here is readability,
I have no objections about correctness.

> +	}
> +
>  	/* convert to rate of irq's per second */
>  	if (ec->rx_coalesce_usecs && ec->rx_coalesce_usecs <= 3)
>  		adapter->rx_itr_setting = ec->rx_coalesce_usecs;
> @@ -921,13 +949,12 @@ static int igc_ethtool_set_coalesce(struct net_device *netdev,
>  		adapter->rx_itr_setting = ec->rx_coalesce_usecs << 2;
>  
>  	/* convert to rate of irq's per second */
> -	if (adapter->flags & IGC_FLAG_QUEUE_PAIRS)
> -		adapter->tx_itr_setting = adapter->rx_itr_setting;
> -	else if (ec->tx_coalesce_usecs && ec->tx_coalesce_usecs <= 3)
> +	if (ec->tx_coalesce_usecs && ec->tx_coalesce_usecs <= 3)
>  		adapter->tx_itr_setting = ec->tx_coalesce_usecs;
>  	else
>  		adapter->tx_itr_setting = ec->tx_coalesce_usecs << 2;
>  
> +program_itr:
>  	for (i = 0; i < adapter->num_q_vectors; i++) {
>  		struct igc_q_vector *q_vector = adapter->q_vector[i];
>  
> -- 
> 2.38.1
> 
>