Re: [PATCH iwl-next v3 04/10] ixgbevf: branch prediction and cleanup

[David Laight <david.laight.linux@gmail.com>]

On Wed,  4 Mar 2026 17:03:36 +0100
Larysa Zaremba <larysa.zaremba@intel.com> wrote:

> Add likely/unlikely markers for better branch prediction. While touching
> some functions, cleanup the code a little bit.
> 
> This patch is not supposed to make any logic changes aside from making
> total_rx_bytes and total_rx_packets more correlated.
> 
> Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
> Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>
> Signed-off-by: Larysa Zaremba <larysa.zaremba@intel.com>
> ---
>  .../net/ethernet/intel/ixgbevf/ixgbevf_main.c | 29 +++++++++----------
>  1 file changed, 14 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c b/drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c
> index 5a270dd2c7aa..4619f2bea1ab 100644
> --- a/drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c
> +++ b/drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c
> @@ -570,7 +570,7 @@ static void ixgbevf_alloc_rx_buffers(struct ixgbevf_ring *rx_ring,
>  	u16 ntu = rx_ring->next_to_use;
>  
>  	/* nothing to do or no valid netdev defined */
> -	if (!cleaned_count || !rx_ring->netdev)
> +	if (unlikely(!cleaned_count || !rx_ring->netdev))
>  		return;
>  
>  	rx_desc = IXGBEVF_RX_DESC(rx_ring, ntu);
> @@ -586,7 +586,7 @@ static void ixgbevf_alloc_rx_buffers(struct ixgbevf_ring *rx_ring,
>  
>  		rx_desc++;
>  		ntu++;
> -		if (unlikely(ntu == rx_ring->count)) {
> +		if (unlikely(ntu == fq.count)) {
>  			rx_desc = IXGBEVF_RX_DESC(rx_ring, 0);
>  			ntu = 0;
>  		}
> @@ -823,7 +823,7 @@ static int ixgbevf_clean_rx_irq(struct ixgbevf_q_vector *q_vector,
>  
>  		rx_desc = IXGBEVF_RX_DESC(rx_ring, rx_ring->next_to_clean);
>  		size = le16_to_cpu(rx_desc->wb.upper.length);
> -		if (!size)
> +		if (unlikely(!size))
>  			break;
>  
>  		/* This memory barrier is needed to keep us from reading
> @@ -855,7 +855,7 @@ static int ixgbevf_clean_rx_irq(struct ixgbevf_q_vector *q_vector,
>  		}
>  
>  		/* exit if we failed to retrieve a buffer */
> -		if (!xdp_res && !skb) {
> +		if (unlikely(!xdp_res && !skb)) {

I'd check that generates something sensible.
Using unlikely on multi-term conditionals doesn't always do
something sensible.

	David

>  			rx_ring->rx_stats.alloc_rx_buff_failed++;
>  			break;
>  		}
> @@ -867,21 +867,19 @@ static int ixgbevf_clean_rx_irq(struct ixgbevf_q_vector *q_vector,
>  			continue;
>  
>  		/* verify the packet layout is correct */
> -		if (xdp_res || ixgbevf_cleanup_headers(rx_ring, rx_desc, skb)) {
> +		if (xdp_res ||
> +		    unlikely(ixgbevf_cleanup_headers(rx_ring, rx_desc, skb))) {
>  			skb = NULL;
>  			continue;
>  		}
>  
> -		/* probably a little skewed due to removing CRC */
> -		total_rx_bytes += skb->len;
> -
>  		/* Workaround hardware that can't do proper VEPA multicast
>  		 * source pruning.
>  		 */
> -		if ((skb->pkt_type == PACKET_BROADCAST ||
> -		     skb->pkt_type == PACKET_MULTICAST) &&
> -		    ether_addr_equal(rx_ring->netdev->dev_addr,
> -				     eth_hdr(skb)->h_source)) {
> +		if (unlikely((skb->pkt_type == PACKET_BROADCAST ||
> +			      skb->pkt_type == PACKET_MULTICAST) &&
> +			     ether_addr_equal(rx_ring->netdev->dev_addr,
> +					      eth_hdr(skb)->h_source))) {
>  			dev_kfree_skb_irq(skb);
>  			continue;
>  		}
> @@ -889,13 +887,14 @@ static int ixgbevf_clean_rx_irq(struct ixgbevf_q_vector *q_vector,
>  		/* populate checksum, VLAN, and protocol */
>  		ixgbevf_process_skb_fields(rx_ring, rx_desc, skb);
>  
> +		/* probably a little skewed due to removing CRC */
> +		total_rx_bytes += skb->len;
> +		total_rx_packets++;
> +
>  		ixgbevf_rx_skb(q_vector, skb);
>  
>  		/* reset skb pointer */
>  		skb = NULL;
> -
> -		/* update budget accounting */
> -		total_rx_packets++;
>  	}
>  
>  	/* place incomplete frames back on ring for completion */