netdev - Re: [PATCH v2 net-next 14/19] ionic: Add Tx and Rx handling

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Message-ID: <20190629115723.5ae777bc@cakuba.netronome.com>
Date:   Sat, 29 Jun 2019 11:57:23 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Shannon Nelson <snelson@...sando.io>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH v2 net-next 14/19] ionic: Add Tx and Rx handling

On Fri, 28 Jun 2019 14:39:29 -0700, Shannon Nelson wrote:
> +static int ionic_tx(struct queue *q, struct sk_buff *skb)
> +{
> +	struct tx_stats *stats = q_to_tx_stats(q);
> +	int err;
> +
> +	if (skb->ip_summed == CHECKSUM_PARTIAL)
> +		err = ionic_tx_calc_csum(q, skb);
> +	else
> +		err = ionic_tx_calc_no_csum(q, skb);
> +	if (err)
> +		return err;
> +
> +	err = ionic_tx_skb_frags(q, skb);
> +	if (err)
> +		return err;
> +
> +	skb_tx_timestamp(skb);
> +	stats->pkts++;
> +	stats->bytes += skb->len;

Presumably this is 64bit so you should use 
u64_stats_update_begin()
u64_stats_update_end() 
around it (and all other stats).

> +
> +	ionic_txq_post(q, !netdev_xmit_more(), ionic_tx_clean, skb);
> +
> +	return 0;
> +}
> +
> +static int ionic_tx_descs_needed(struct queue *q, struct sk_buff *skb)
> +{
> +	struct tx_stats *stats = q_to_tx_stats(q);
> +	int err;
> +
> +	/* If TSO, need roundup(skb->len/mss) descs */
> +	if (skb_is_gso(skb))
> +		return (skb->len / skb_shinfo(skb)->gso_size) + 1;
> +
> +	/* If non-TSO, just need 1 desc and nr_frags sg elems */
> +	if (skb_shinfo(skb)->nr_frags <= IONIC_TX_MAX_SG_ELEMS)
> +		return 1;
> +
> +	/* Too many frags, so linearize */
> +	err = skb_linearize(skb);
> +	if (err)
> +		return err;
> +
> +	stats->linearize++;
> +
> +	/* Need 1 desc and zero sg elems */
> +	return 1;
> +}
> +
> +netdev_tx_t ionic_start_xmit(struct sk_buff *skb, struct net_device *netdev)
> +{
> +	u16 queue_index = skb_get_queue_mapping(skb);
> +	struct lif *lif = netdev_priv(netdev);
> +	struct queue *q;
> +	int ndescs;
> +	int err;
> +
> +	if (unlikely(!test_bit(LIF_UP, lif->state))) {
> +		dev_kfree_skb(skb);
> +		return NETDEV_TX_OK;
> +	}
> +
> +	if (likely(lif_to_txqcq(lif, queue_index)))
> +		q = lif_to_txq(lif, queue_index);
> +	else
> +		q = lif_to_txq(lif, 0);
> +
> +	ndescs = ionic_tx_descs_needed(q, skb);
> +	if (ndescs < 0)
> +		goto err_out_drop;
> +
> +	if (!ionic_q_has_space(q, ndescs)) {
> +		netif_stop_subqueue(netdev, queue_index);
> +		q->stop++;
> +
> +		/* Might race with ionic_tx_clean, check again */
> +		smp_rmb();
> +		if (ionic_q_has_space(q, ndescs)) {
> +			netif_wake_subqueue(netdev, queue_index);
> +			q->wake++;
> +		} else {
> +			return NETDEV_TX_BUSY;

This should never really happen..

> +		}
> +	}
> +
> +	if (skb_is_gso(skb))
> +		err = ionic_tx_tso(q, skb);
> +	else
> +		err = ionic_tx(q, skb);
> +
> +	if (err)
> +		goto err_out_drop;

.. at this point if you can't guarantee fitting biggest possible frame
in, you have to stop the ring.

> +	return NETDEV_TX_OK;
> +
> +err_out_drop:
> +	q->drop++;
> +	dev_kfree_skb(skb);
> +	return NETDEV_TX_OK;
> +}