From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ben Hutchings <bhutchings@solarflare.com>
Subject: Re: [RFC] [PATCH] net: Add support for
	ndo_select_queue()	functions to cache the queue mapping
Date: Thu, 28 Jan 2010 18:40:59 +0000
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Cc: linux-net-drivers@solarflare.com, netdev@vger.kernel.org
To: Krishna Kumar2 <krkumar2@in.ibm.com>
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On Fri, 2010-01-29 at 00:11 +0530, Krishna Kumar2 wrote:
> > Ben Hutchings <bhutchings@solarflare.com>
> >
> > On Thu, 2010-01-28 at 23:39 +0530, Krishna Kumar2 wrote:
[...]
> > > Other than that, I saw netif_sk_tx_queue_set is not called.
> > > And dev_pick_tx has already capped automatically, you probably
> > > don't need another here?
> >
> > Only the return value of ndo_select_queue() is capped; the cached value
> > is assumed to be valid.
> 
> +void netif_sk_tx_queue_set(struct net_device *dev, struct sock *sk,
> +                             u16 queue_index)
> +{
> +     sk_tx_queue_set(sk, dev_cap_txqueue(dev, queue_index));
> +}
> 
> I guess I didn't understand this then, who calls this function?
[...]

The driver's ndo_select_queue() implementation calls it before
returning, if and only if sk_may_set_tx_queue() is true and its
selection is dependent only on the flow id.

As an example, ixgbe's selection function:

        static u16 ixgbe_select_queue(struct net_device *dev, struct sk_buff *skb)
        {
        	struct ixgbe_adapter *adapter = netdev_priv(dev);
        	int txq = smp_processor_id();
        
        	if (adapter->flags & IXGBE_FLAG_FDIR_HASH_CAPABLE)
        		return txq;
        
        #ifdef IXGBE_FCOE
        	if ((adapter->flags & IXGBE_FLAG_FCOE_ENABLED) &&
        	    (skb->protocol == htons(ETH_P_FCOE))) {
        		txq &= (adapter->ring_feature[RING_F_FCOE].indices - 1);
        		txq += adapter->ring_feature[RING_F_FCOE].mask;
        		return txq;
        	}
        #endif
        	if (adapter->flags & IXGBE_FLAG_DCB_ENABLED)
        		return (skb->vlan_tci & IXGBE_TX_FLAGS_VLAN_PRIO_MASK) >> 13;
        
        	return skb_tx_hash(dev, skb);
        }
        
would not call netif_sk_tx_queue_set() in the first two cases, but could
do so in the last two cases if sk_may_set_tx_queue(skb->sk) is true.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.