Subject: Re: [PATCH 2/2] pktgen: introduce xmit_mode 'rx_inject'

From: Alexander Duyck <[email-masked]>
Date: Tue, 05 May 2015 22:32:34 -0700

On 05/05/2015 01:30 PM, Jesper Dangaard Brouer wrote:

<snip>

> diff --git a/net/core/pktgen.c b/net/core/pktgen.c
> index 43bb215..85195b2 100644
> --- a/net/core/pktgen.c
> +++ b/net/core/pktgen.c
> @@ -210,6 +210,10 @@

<snip>

> @@ -3320,6 +3358,7 @@ static void pktgen_xmit(struct pktgen_dev *pkt_dev)
>   	unsigned int burst = ACCESS_ONCE(pkt_dev->burst);
>   	struct net_device *odev = pkt_dev->odev;
>   	struct netdev_queue *txq;
> +	struct sk_buff *skb;
>   	int ret;
>
>   	/* If device is offline, then don't send */
> @@ -3352,11 +3391,45 @@ static void pktgen_xmit(struct pktgen_dev *pkt_dev)
>   		pkt_dev->last_pkt_size = pkt_dev->skb->len;
>   		pkt_dev->allocated_skbs++;
>   		pkt_dev->clone_count = 0;	/* reset counter */
> +		if (pkt_dev->xmit_mode == M_RX_INJECT)
> +			pkt_dev->skb->protocol = eth_type_trans(pkt_dev->skb,
> +								pkt_dev->skb->dev);
>   	}
>

I was just wondering.  Since M_RX_INJECT is not compatible with 
clone_skb couldn't the lines added above be moved down into the block 
below so that you could avoid the additional conditional jump?

>   	if (pkt_dev->delay && pkt_dev->last_ok)
>   		spin(pkt_dev, pkt_dev->next_tx);
>
> +	if (pkt_dev->xmit_mode == M_RX_INJECT) {
> +		skb = pkt_dev->skb;
> +		atomic_add(burst, &skb->users);
> +		local_bh_disable();
> +		do {
> +			ret = netif_receive_skb(skb);
> +			if (ret == NET_RX_DROP)
> +				pkt_dev->errors++;
> +			pkt_dev->sofar++;
> +			pkt_dev->seq_num++;
> +			if (atomic_read(&skb->users) != burst) {
> +				/* skb was queued by rps/rfs or taps,
> +				 * so cannot reuse this skb
> +				 */
> +				atomic_sub(burst - 1, &skb->users);
> +				/* get out of the loop and wait
> +				 * until skb is consumed
> +				 */
> +				pkt_dev->last_ok = 1;
> +				break;
> +			}
> +			/* skb was 'freed' by stack, so clean few
> +			 * bits and reuse it
> +			 */
> +#ifdef CONFIG_NET_CLS_ACT
> +			skb->tc_verd = 0; /* reset reclass/redir ttl */
> +#endif
> +		} while (--burst > 0);
> +		goto out; /* Skips xmit_mode M_TX */
> +	}
> +
>   	txq = skb_get_tx_queue(odev, pkt_dev->skb);
>
>   	local_bh_disable();
> @@ -3404,6 +3477,7 @@ xmit_more:
>   unlock:
>   	HARD_TX_UNLOCK(odev, txq);
>
> +out:
>   	local_bh_enable();
>
>   	/* If pkt_dev->count is zero, then run forever */
>
> --
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