netdev - Re: [PATCH net-next] tun: compute the RFS hash only if needed.

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Date:   Wed, 7 Nov 2018 21:33:24 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next] tun: compute the RFS hash only if needed.


On 2018/11/7 下午5:34, Paolo Abeni wrote:
> The tun XDP sendmsg code path, unconditionally computes the symmetric
> hash of each packet for RFS's sake, even when we could skip it. e.g.
> when the device has a single queue.
>
> This change adds the check already in-place for the skb sendmsg path
> to avoid unneeded hashing.
>
> The above gives small, but measurable, performance gain for VM xmit
> path when zerocopy is not enabled.
>
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> ---
>   drivers/net/tun.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 060135ceaf0e..a65779c6d72f 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -2448,7 +2448,8 @@ static int tun_xdp_one(struct tun_struct *tun,
>   			goto out;
>   	}
>   
> -	if (!rcu_dereference(tun->steering_prog))
> +	if (!rcu_dereference(tun->steering_prog) && tun->numqueues > 1 &&
> +	    !tfile->detached)
>   		rxhash = __skb_get_hash_symmetric(skb);
>   
>   	netif_receive_skb(skb);


Acked-by: Jason Wang <jasowang@...hat.com>

Thanks