netdev - Re: [PATCH net-next 1/2] net: tap: replay while() loop with % operator in tap_get

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Date:   Mon, 11 Dec 2017 08:58:11 -0800
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     yuan linyu <cugyly@....com>
Cc:     netdev@...r.kernel.org, "David S . Miller" <davem@...emloft.net>,
        yuan linyu <Linyu.Yuan@...atel-sbell.com.cn>
Subject: Re: [PATCH net-next 1/2] net: tap: replay while() loop with %
 operator in tap_get_queue()

On Mon, 11 Dec 2017 21:26:41 +0800
yuan linyu <cugyly@....com> wrote:

> From: yuan linyu <Linyu.Yuan@...atel-sbell.com.cn>
> 
> Signed-off-by: yuan linyu <Linyu.Yuan@...atel-sbell.com.cn>
> ---
>  drivers/net/tap.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/drivers/net/tap.c b/drivers/net/tap.c
> index 0a886fda..78900a0 100644
> --- a/drivers/net/tap.c
> +++ b/drivers/net/tap.c
> @@ -275,11 +275,7 @@ static struct tap_queue *tap_get_queue(struct tap_dev *tap,
>  
>  	if (likely(skb_rx_queue_recorded(skb))) {
>  		rxq = skb_get_rx_queue(skb);
> -
> -		while (unlikely(rxq >= numvtaps))
> -			rxq -= numvtaps;
> -
> -		queue = rcu_dereference(tap->taps[rxq]);
> +		queue = rcu_dereference(tap->taps[rxq % numvtaps]);
>  		goto out;
>  	}
>  

Modulus is slower than the loop.