netdev - Re: [PATCH 3/3] net: allocate tx queues in register

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Message-ID: <1287438080.2252.792.camel@achroite.uk.solarflarecom.com>
Date:	Mon, 18 Oct 2010 22:41:20 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	eric.dumazet@...il.com, John Fastabend <john.r.fastabend@...el.com>
Subject: Re: [PATCH 3/3] net: allocate tx queues in register_netdevice

On Mon, 2010-10-18 at 11:02 -0700, Tom Herbert wrote:
> This patch introduces netif_alloc_netdev_queues which is called from
> register_device instead of alloc_netdev_mq.  This makes TX queue
> allocation symmetric with RX allocation similarly allows drivers to
> change dev->num_tx_queues after allocating netdev and before
> registering it.

Changing num_tx_queues is probably *not* desirable, same as for
num_rx_queues.

[...]
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -1553,18 +1553,24 @@ static void dev_queue_xmit_nit(struct sk_buff *skb, struct net_device *dev)
>   * Routine to help set real_num_tx_queues. To avoid skbs mapped to queues
>   * greater then real_num_tx_queues stale skbs on the qdisc must be flushed.
>   */
> -void netif_set_real_num_tx_queues(struct net_device *dev, unsigned int txq)
> +int netif_set_real_num_tx_queues(struct net_device *dev, unsigned int txq)
>  {
> -	unsigned int real_num = dev->real_num_tx_queues;
> +	if (txq < 1)
> +		return -EINVAL;
>  
> -	if (unlikely(txq > dev->num_tx_queues))
> -		;
> -	else if (txq > real_num)
> -		dev->real_num_tx_queues = txq;
> -	else if (txq < real_num) {
> -		dev->real_num_tx_queues = txq;
> -		qdisc_reset_all_tx_gt(dev, txq);
> -	}
> +	if (dev->reg_state == NETREG_REGISTERED) {
> +		ASSERT_RTNL();
> +
> +		if (txq > dev->num_tx_queues)
> +			return -EINVAL;
> +
> +		if (txq < dev->real_num_tx_queues)
> +			qdisc_reset_all_tx_gt(dev, txq);
> +	} else
> +		dev->num_tx_queues = txq;
[...]

The kernel-doc comment should be updated to reflect the locking
requirement and the possibility of failure when called after
registration.

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.

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