Subject: Re: [PATCH 2/4] macvlan: cleanup rx statistics

From: Eric Dumazet <[email-masked]>
Date: Tue, 24 Nov 2009 09:15:53 +0100

Arnd Bergmann a écrit :
> We have very similar code for rx statistics in
> two places in the macvlan driver, with a third
> one being added in the next patch.
> 
> Consolidate them into one function to improve
> overall readability of the driver.
> 
> Signed-off-by: Arnd Bergmann <[email-masked]>
> ---
>  drivers/net/macvlan.c |   63 +++++++++++++++++++++++++-----------------------
>  1 files changed, 33 insertions(+), 30 deletions(-)
> 
> diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
> index ae2b5c7..a0dea23 100644
> --- a/drivers/net/macvlan.c
> +++ b/drivers/net/macvlan.c
> @@ -116,42 +116,53 @@ static int macvlan_addr_busy(const struct macvlan_port *port,
>  	return 0;
>  }
>  
> +static inline void macvlan_count_rx(const struct macvlan_dev *vlan, int length,
> +			     int success, int multicast)

success and multicast should be declared as bool

> +{
> +	struct macvlan_rx_stats *rx_stats;
> +
> +	rx_stats = per_cpu_ptr(vlan->rx_stats, smp_processor_id());
> +	rx_stats->rx_packets += success != 0;
> +	rx_stats->rx_bytes   += success ? length : 0;
> +	rx_stats->multicast  += success && multicast;
> +	rx_stats->rx_errors  += !success;
> +}
> +

I find following more readable, it probably generates more branches,
but avoid dirtying rx_errors if it is in another cache line.

if (likely(success)) {
	rx_stats->rx_packets++;
	rx_stats->rx_bytes += length;
	if (multicast)
		rx_stats->multicast++;
} else {
	rx_stats->rx_errors++;
}

> -	rx_stats = per_cpu_ptr(vlan->rx_stats, smp_processor_id());
>  	skb = skb_share_check(skb, GFP_ATOMIC);
> -	if (skb == NULL) {
> -		rx_stats->rx_errors++;
> -		return NULL;
> -	}
> -
> -	rx_stats->rx_bytes += skb->len + ETH_HLEN;
> -	rx_stats->rx_packets++;
> +	macvlan_count_rx(vlan, skb->len + ETH_HLEN, likely(skb != NULL), 0);

its not _likely_ that skb != NULL, its a fact :)

-> macvlan_count_rx(vlan, skb->len + ETH_HLEN, true, false);