netdev - Re: [PATCH] net: core: improve the tx

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Date:   Fri, 1 Jun 2018 05:54:24 -0400
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Tonghao Zhang <xiangxia.m.yue@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH] net: core: improve the tx_hash calculating



On 05/31/2018 06:14 AM, Tonghao Zhang wrote:
> Use the % instead of while, and it may simple code and improve
> the calculating. The real_num_tx_queues has been checked when
> allocating and setting it.
> 
> Signed-off-by: Tonghao Zhang <xiangxia.m.yue@...il.com>
> ---
>  net/core/dev.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 1844d9b..edc5b75 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -2617,15 +2617,13 @@ void netif_device_attach(struct net_device *dev)
>   */
>  static u16 skb_tx_hash(const struct net_device *dev, struct sk_buff *skb)
>  {
> -	u32 hash;
>  	u16 qoffset = 0;
>  	u16 qcount = dev->real_num_tx_queues;
>  
>  	if (skb_rx_queue_recorded(skb)) {
> -		hash = skb_get_rx_queue(skb);
> -		while (unlikely(hash >= qcount))
> -			hash -= qcount;
> -		return hash;
> +		/* When setting the real_num_tx_queues, we make sure
> +		 * real_num_tx_queues != 0. */
> +		return skb_get_rx_queue(skb) % qcount;
>  	}
>  
>  	if (dev->num_tc) {
> 


This patch is adding a divide. We do not need it most of the time.