Subject: Re: [patch 37/44] xen: add virtual network device driver

From: Stephen Hemminger <[email-masked]>
Date: Tue, 17 Jul 2007 09:45:11 +0100

> +struct netfront_info {
> +	struct list_head list;
> +	struct net_device *netdev;
> +
> +	struct net_device_stats stats;

There is now a net_device_stats element inside net_device on
2.6.21 or later.

> +
> +	struct xen_netif_tx_front_ring tx;
> +	struct xen_netif_rx_front_ring rx;
> +
> +	spinlock_t   tx_lock;
> +	spinlock_t   rx_lock;

It might be a performance advantage to reorder/align these
structure elements to put transmit hot elements together, and
put tx and rx on different cache lines?

> +	unsigned int evtchn;
> +
> +	/* Receive-ring batched refills. */
> +#define RX_MIN_TARGET 8
> +#define RX_DFL_MIN_TARGET 64
> +#define RX_MAX_TARGET min_t(int, NET_RX_RING_SIZE, 256)
> +	unsigned rx_min_target, rx_max_target, rx_target;
> +	struct sk_buff_head rx_batch;
> +
> +	struct timer_list rx_refill_timer;
> +
> +	/*
> +	 * {tx,rx}_skbs store outstanding skbuffs. Free tx_skb entries
> +	 * are linked from tx_skb_freelist through skb_entry.link.
> +	 *
> +	 *  NB. Freelist index entries are always going to be less than
> +	 *  PAGE_OFFSET, whereas pointers to skbs will always be equal or
> +	 *  greater than PAGE_OFFSET: we use this property to distinguish
> +	 *  them.
> +	 */
> +	union skb_entry {
> +		struct sk_buff *skb;
> +		unsigned link;
> +	} tx_skbs[NET_TX_RING_SIZE];
> +	grant_ref_t gref_tx_head;
> +	grant_ref_t grant_tx_ref[NET_TX_RING_SIZE];
> +	unsigned tx_skb_freelist;
> +
> +	struct sk_buff *rx_skbs[NET_RX_RING_SIZE];
> +	grant_ref_t gref_rx_head;
> +	grant_ref_t grant_rx_ref[NET_RX_RING_SIZE];
> +
> +	struct xenbus_device *xbdev;
> +	int tx_ring_ref;
> +	int rx_ring_ref;
> +
> +	unsigned long rx_pfn_array[NET_RX_RING_SIZE];
> +	struct multicall_entry rx_mcl[NET_RX_RING_SIZE+1];
> +	struct mmu_update rx_mmu[NET_RX_RING_SIZE];
> +};