netdev - Re: [net-next 5/5] ixgbe: convert to ndo_fix

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Date:	Tue, 12 Jul 2011 23:44:45 +0200
From:	Michal Miroslaw <mirq-linux@...e.qmqm.pl>
To:	"Skidmore, Donald C" <donald.c.skidmore@...el.com>
Cc:	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"gospo@...hat.com" <gospo@...hat.com>
Subject: Re: [net-next 5/5] ixgbe: convert to ndo_fix_features

Good to see the idea converging. :) More hints below.

On Tue, Jul 12, 2011 at 02:28:15PM -0700, Skidmore, Donald C wrote:
[...]
> The logic in this conditional is a little complex. I believe it would
> end up looking something like the following:
> 
> in fix_features:
> 
> 	/* Prevent change if not RSC capable or invalid ITR setting */
> 	if (data & NETIF_F_LRO)

That's not a fast path - you can drop (data & NETIF_F_LRO) check.

> 		if (!(adapter->flags2 & IXGBE_FLAG2_RSC_CAPABLE) {
> 			data &= ~NETIF_F_LRO;
> 		else if (!(adapter->flags2 & IXGBE_FLAG2_RSC_ENABLED) &&
> 	    		   (adapter->rx_itr_setting != 1 &&
> 			    adapter->rx_itr_setting > IXGBE_MAX_RSC_INT_RATE)) {
> 				data &= ~NETIF_F_LRO;
> 		}
> 	} 

Same for !(adapter->flags2 & IXGBE_FLAG2_RSC_ENABLED). After this change,
you might add a call to netdev_update_features() whenever the second part
of the condition is changed by user and you get correctness all the time
'for free'.

> in set_feature:
> 
> 	/* Make sure RSC matches LRO, reset if change */
> 	if (!!(data & NETIF_F_LRO) != 
> 	    !!(adapter->flags2 & IXGBE_FLAG2_RSC_ENABLED)) {
> 		adapter->flags2 ^= IXGBE_FLAG2_RSC_ENABLED;
> 		switch (adapter->hw.mac.type) {
> 		case ixgbe_mac_X540:
> 		case ixgbe_mac_82599EB:
> 			need_reset = true;
> 			break;
> 		default:
> 			break;	
> 		}
> 	}

Correct. Why would you need IXGBE_FLAG2_RSC_ENABLED now, when it just
mirrors NETIF_F_LRO?

[...]
> Thanks again for the clarifications, the netdev-features.txt helped a lot too. 

Nice to hear (read) that!

Best Regards,
Michał Mirosław
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