Date:   Tue, 10 Jan 2023 08:56:12 -0800
From:   Alexander H Duyck <alexander.duyck@...il.com>
To:     Gerhard Engleder <gerhard@...leder-embedded.com>,
        netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, edumazet@...gle.com,
        pabeni@...hat.com
Subject: Re: [PATCH net-next v4 05/10] tsnep: Add XDP TX support

nOn Mon, 2023-01-09 at 20:15 +0100, Gerhard Engleder wrote:
> Implement ndo_xdp_xmit() for XDP TX support. Support for fragmented XDP
> frames is included.
> 
> Also some const, braces and logic clean ups are done in normal TX path
> to keep both TX paths in sync.
> 
> Signed-off-by: Gerhard Engleder <gerhard@...leder-embedded.com>
> ---
>  drivers/net/ethernet/engleder/tsnep.h      |  12 +-
>  drivers/net/ethernet/engleder/tsnep_main.c | 211 +++++++++++++++++++--
>  2 files changed, 210 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/net/ethernet/engleder/tsnep.h b/drivers/net/ethernet/engleder/tsnep.h
> index d658413ceb14..9cb267938794 100644
> --- a/drivers/net/ethernet/engleder/tsnep.h
> +++ b/drivers/net/ethernet/engleder/tsnep.h
> @@ -57,6 +57,12 @@ struct tsnep_rxnfc_rule {
>  	int location;
>  };
>  
> +enum tsnep_tx_type {
> +	TSNEP_TX_TYPE_SKB,
> +	TSNEP_TX_TYPE_XDP_TX,
> +	TSNEP_TX_TYPE_XDP_NDO,
> +};
> +

I'm more a fan of using a bitmap rather than an enum for these type of
things since otherwise you are having to check for 3 possible values
for everything.

Also you may want to reorder this so that SKB is the last option. With
that 0/1 would be your two XDP values and 2 would be your SKB value. It
should make it easier for this to be treated more as a decision tree.

>  struct tsnep_tx_entry {
>  	struct tsnep_tx_desc *desc;
>  	struct tsnep_tx_desc_wb *desc_wb;
> @@ -65,7 +71,11 @@ struct tsnep_tx_entry {
>  
>  	u32 properties;
>  
> -	struct sk_buff *skb;
> +	enum tsnep_tx_type type;
> +	union {
> +		struct sk_buff *skb;
> +		struct xdp_frame *xdpf;
> +	};
>  	size_t len;
>  	DEFINE_DMA_UNMAP_ADDR(dma);
>  };
> diff --git a/drivers/net/ethernet/engleder/tsnep_main.c b/drivers/net/ethernet/engleder/tsnep_main.c
> index 943de5a09693..1ae73c706c9e 100644
> --- a/drivers/net/ethernet/engleder/tsnep_main.c
> +++ b/drivers/net/ethernet/engleder/tsnep_main.c
> @@ -310,10 +310,12 @@ static void tsnep_tx_activate(struct tsnep_tx *tx, int index, int length,
>  	struct tsnep_tx_entry *entry = &tx->entry[index];
>  
>  	entry->properties = 0;
> +	/* xdpf is union with skb */
>  	if (entry->skb) {
>  		entry->properties = length & TSNEP_DESC_LENGTH_MASK;
>  		entry->properties |= TSNEP_DESC_INTERRUPT_FLAG;
> -		if (skb_shinfo(entry->skb)->tx_flags & SKBTX_IN_PROGRESS)
> +		if (entry->type == TSNEP_TX_TYPE_SKB &&
> +		    (skb_shinfo(entry->skb)->tx_flags & SKBTX_IN_PROGRESS))
>  			entry->properties |= TSNEP_DESC_EXTENDED_WRITEBACK_FLAG;
>  
>  		/* toggle user flag to prevent false acknowledge
> @@ -370,7 +372,8 @@ static int tsnep_tx_desc_available(struct tsnep_tx *tx)
>  		return tx->read - tx->write - 1;
>  }
>  
> -static int tsnep_tx_map(struct sk_buff *skb, struct tsnep_tx *tx, int count)
> +static int tsnep_tx_map(const struct sk_buff *skb, struct tsnep_tx *tx,
> +			int count)
>  {

This change to const doesn't add anything since this is a static
function. You could probably just skip making this change since the
function will likely be inlined anyway.

>  	struct device *dmadev = tx->adapter->dmadev;
>  	struct tsnep_tx_entry *entry;
> @@ -382,7 +385,7 @@ static int tsnep_tx_map(struct sk_buff *skb, struct tsnep_tx *tx, int count)
>  	for (i = 0; i < count; i++) {
>  		entry = &tx->entry[(tx->write + i) % TSNEP_RING_SIZE];
>  
> -		if (i == 0) {
> +		if (!i) {
>  			len = skb_headlen(skb);
>  			dma = dma_map_single(dmadev, skb->data, len,
>  					     DMA_TO_DEVICE);
> @@ -400,6 +403,8 @@ static int tsnep_tx_map(struct sk_buff *skb, struct tsnep_tx *tx, int count)
>  
>  		entry->desc->tx = __cpu_to_le64(dma);
>  
> +		entry->type = TSNEP_TX_TYPE_SKB;
> +
>  		map_len += len;
>  	}
>  

I wonder if it wouldn't be better to change this so that you have a 4th
type for just "PAGE" or "FRAGMENT" since you only really need to
identify this as SKB or XDP on the first buffer, and then all the rest
are just going to be unmapped as page regardless of if it is XDP or
SKB.

> @@ -417,12 +422,13 @@ static int tsnep_tx_unmap(struct tsnep_tx *tx, int index, int count)
>  		entry = &tx->entry[(index + i) % TSNEP_RING_SIZE];
>  
>  		if (entry->len) {
> -			if (i == 0)
> +			if (!i && entry->type == TSNEP_TX_TYPE_SKB)
>  				dma_unmap_single(dmadev,
>  						 dma_unmap_addr(entry, dma),
>  						 dma_unmap_len(entry, len),
>  						 DMA_TO_DEVICE);
> -			else
> +			else if (entry->type == TSNEP_TX_TYPE_SKB ||
> +				 entry->type == TSNEP_TX_TYPE_XDP_NDO)
>  				dma_unmap_page(dmadev,
>  					       dma_unmap_addr(entry, dma),
>  					       dma_unmap_len(entry, len),

Rather than perform 2 checks here you could just verify type !=
TYPE_XDP_TX which would save you a check.

> @@ -482,7 +488,7 @@ static netdev_tx_t tsnep_xmit_frame_ring(struct sk_buff *skb,
>  
>  	for (i = 0; i < count; i++)
>  		tsnep_tx_activate(tx, (tx->write + i) % TSNEP_RING_SIZE, length,
> -				  i == (count - 1));
> +				  i == count - 1);
>  	tx->write = (tx->write + count) % TSNEP_RING_SIZE;
>  
>  	skb_tx_timestamp(skb);
> @@ -502,12 +508,133 @@ static netdev_tx_t tsnep_xmit_frame_ring(struct sk_buff *skb,
>  	return NETDEV_TX_OK;
>  }
>  
> +static int tsnep_xdp_tx_map(const struct xdp_frame *xdpf, struct tsnep_tx *tx,
> +			    const struct skb_shared_info *shinfo, int count,
> +			    enum tsnep_tx_type type)

Again the const here isn't adding any value since this is a static
function and will likely be inlined into the function below which calls
it.

> +{
> +	struct device *dmadev = tx->adapter->dmadev;
> +	struct tsnep_tx_entry *entry;
> +	const skb_frag_t *frag;
> +	struct page *page;
> +	unsigned int len;
> +	int map_len = 0;
> +	dma_addr_t dma;
> +	void *data;
> +	int i;
> +
> +	frag = NULL;
> +	len = xdpf->len;
> +	for (i = 0; i < count; i++) {
> +		entry = &tx->entry[(tx->write + i) % TSNEP_RING_SIZE];
> +		if (type == TSNEP_TX_TYPE_XDP_NDO) {
> +			data = unlikely(frag) ? skb_frag_address(frag) :
> +						xdpf->data;
> +			dma = dma_map_single(dmadev, data, len, DMA_TO_DEVICE);
> +			if (dma_mapping_error(dmadev, dma))
> +				return -ENOMEM;
> +
> +			entry->type = TSNEP_TX_TYPE_XDP_NDO;
> +		} else {
> +			page = unlikely(frag) ? skb_frag_page(frag) :
> +						virt_to_page(xdpf->data);
> +			dma = page_pool_get_dma_addr(page);
> +			if (unlikely(frag))
> +				dma += skb_frag_off(frag);
> +			else
> +				dma += sizeof(*xdpf) + xdpf->headroom;
> +			dma_sync_single_for_device(dmadev, dma, len,
> +						   DMA_BIDIRECTIONAL);
> +
> +			entry->type = TSNEP_TX_TYPE_XDP_TX;
> +		}
> +
> +		entry->len = len;
> +		dma_unmap_addr_set(entry, dma, dma);
> +
> +		entry->desc->tx = __cpu_to_le64(dma);
> +
> +		map_len += len;
> +
> +		if (i + 1 < count) {
> +			frag = &shinfo->frags[i];
> +			len = skb_frag_size(frag);
> +		}
> +	}
> +
> +	return map_len;
> +}
> +
> +/* This function requires __netif_tx_lock is held by the caller. */
> +static bool tsnep_xdp_xmit_frame_ring(struct xdp_frame *xdpf,
> +				      struct tsnep_tx *tx,
> +				      enum tsnep_tx_type type)
> +{
> +	const struct skb_shared_info *shinfo =
> +		xdp_get_shared_info_from_frame(xdpf);
> +	struct tsnep_tx_entry *entry;
> +	int count, length, retval, i;
> +
> +	count = 1;
> +	if (unlikely(xdp_frame_has_frags(xdpf)))
> +		count += shinfo->nr_frags;
> +
> +	spin_lock_bh(&tx->lock);
> +
> +	/* ensure that TX ring is not filled up by XDP, always MAX_SKB_FRAGS
> +	 * will be available for normal TX path and queue is stopped there if
> +	 * necessary
> +	 */
> +	if (tsnep_tx_desc_available(tx) < (MAX_SKB_FRAGS + 1 + count)) {
> +		spin_unlock_bh(&tx->lock);
> +
> +		return false;
> +	}
> +
> +	entry = &tx->entry[tx->write];
> +	entry->xdpf = xdpf;
> +
> +	retval = tsnep_xdp_tx_map(xdpf, tx, shinfo, count, type);
> +	if (retval < 0) {
> +		tsnep_tx_unmap(tx, tx->write, count);
> +		entry->xdpf = NULL;
> +
> +		tx->dropped++;
> +
> +		spin_unlock_bh(&tx->lock);
> +
> +		return false;
> +	}
> +	length = retval;
> +
> +	for (i = 0; i < count; i++)
> +		tsnep_tx_activate(tx, (tx->write + i) % TSNEP_RING_SIZE, length,
> +				  i == count - 1);
> +	tx->write = (tx->write + count) % TSNEP_RING_SIZE;
> +
> +	/* descriptor properties shall be valid before hardware is notified */
> +	dma_wmb();
> +
> +	spin_unlock_bh(&tx->lock);
> +
> +	return true;
> +}
> +
> +static void tsnep_xdp_xmit_flush(struct tsnep_tx *tx)
> +{
> +	iowrite32(TSNEP_CONTROL_TX_ENABLE, tx->addr + TSNEP_CONTROL);
> +}
> +
>  static bool tsnep_tx_poll(struct tsnep_tx *tx, int napi_budget)
>  {
> -	int budget = 128;
>  	struct tsnep_tx_entry *entry;
> -	int count;
> +	struct xdp_frame_bulk bq;
> +	int budget = 128;
>  	int length;
> +	int count;
> +
> +	xdp_frame_bulk_init(&bq);
> +
> +	rcu_read_lock(); /* need for xdp_return_frame_bulk */
>  

You should be able to get rid of both of these. See comments below.

>  	spin_lock_bh(&tx->lock);
>  
> @@ -527,12 +654,17 @@ static bool tsnep_tx_poll(struct tsnep_tx *tx, int napi_budget)
>  		dma_rmb();
>  
>  		count = 1;
> -		if (skb_shinfo(entry->skb)->nr_frags > 0)
> +		if (entry->type == TSNEP_TX_TYPE_SKB &&
> +		    skb_shinfo(entry->skb)->nr_frags > 0)
>  			count += skb_shinfo(entry->skb)->nr_frags;
> +		else if (entry->type != TSNEP_TX_TYPE_SKB &&
> +			 xdp_frame_has_frags(entry->xdpf))
> +			count += xdp_get_shared_info_from_frame(entry->xdpf)->nr_frags;
>  
>  		length = tsnep_tx_unmap(tx, tx->read, count);
>  
> -		if ((skb_shinfo(entry->skb)->tx_flags & SKBTX_IN_PROGRESS) &&
> +		if (entry->type == TSNEP_TX_TYPE_SKB &&
> +		    (skb_shinfo(entry->skb)->tx_flags & SKBTX_IN_PROGRESS) &&
>  		    (__le32_to_cpu(entry->desc_wb->properties) &
>  		     TSNEP_DESC_EXTENDED_WRITEBACK_FLAG)) {
>  			struct skb_shared_hwtstamps hwtstamps;
> @@ -552,7 +684,18 @@ static bool tsnep_tx_poll(struct tsnep_tx *tx, int napi_budget)
>  			skb_tstamp_tx(entry->skb, &hwtstamps);
>  		}
>  
> -		napi_consume_skb(entry->skb, napi_budget);
> +		switch (entry->type) {
> +		case TSNEP_TX_TYPE_SKB:
> +			napi_consume_skb(entry->skb, napi_budget);
> +			break;
> +		case TSNEP_TX_TYPE_XDP_TX:
> +			xdp_return_frame_rx_napi(entry->xdpf);
> +			break;
> +		case TSNEP_TX_TYPE_XDP_NDO:
> +			xdp_return_frame_bulk(entry->xdpf, &bq);
> +			break;
> +		}
> +		/* xdpf is union with skb */
>  		entry->skb = NULL;
>  
>  		tx->read = (tx->read + count) % TSNEP_RING_SIZE;

If I am not mistaken I think you can use xdp_return_frame_rx_napi for
both of these without having to resort to the bulk approach since the
tsnep_tx_poll is operating in the NAPI polling context.

When you free the buffers outside of polling context you would then
want to use the xdp_return_frame_bulk. So for example if you have any
buffers that weren't transmitted when you get to the point of
tsnep_tx_ring_cleanup then you would want to unmap and free them there
using something like the xdp_return_frame or xdp_return_frame_bulk.

> @@ -570,7 +713,11 @@ static bool tsnep_tx_poll(struct tsnep_tx *tx, int napi_budget)
>  
>  	spin_unlock_bh(&tx->lock);
>  
> -	return (budget != 0);
> +	xdp_flush_frame_bulk(&bq);
> +
> +	rcu_read_unlock();
> +
> +	return budget != 0;
>  }
>  
>  static bool tsnep_tx_pending(struct tsnep_tx *tx)
> @@ -1330,6 +1477,45 @@ static ktime_t tsnep_netdev_get_tstamp(struct net_device *netdev,
>  	return ns_to_ktime(timestamp);
>  }
>  
> +static int tsnep_netdev_xdp_xmit(struct net_device *dev, int n,
> +				 struct xdp_frame **xdp, u32 flags)
> +{
> +	struct tsnep_adapter *adapter = netdev_priv(dev);
> +	u32 cpu = smp_processor_id();
> +	struct netdev_queue *nq;
> +	int nxmit, queue;
> +	bool xmit;
> +
> +	if (unlikely(test_bit(__TSNEP_DOWN, &adapter->state)))
> +		return -ENETDOWN;
> +

Again, here you are better off probably checking for netif_carrier_ok
rather than adding a new flag.

> +	if (unlikely(flags & ~XDP_XMIT_FLAGS_MASK))
> +		return -EINVAL;
> +
> +	queue = cpu % adapter->num_tx_queues;

Modulo math here unconditionally will be expensive. Take a look at
using reciprocal_scale like we do in skb_tx_hash.

> +	nq = netdev_get_tx_queue(adapter->netdev, queue);
> +
> +	__netif_tx_lock(nq, cpu);
> +
> +	/* Avoid transmit queue timeout since we share it with the slow path */
> +	txq_trans_cond_update(nq);
> +

Doing this here may not be the right spot. It might make more sense to
do this after the call to xmit_frame_ring after the break case in order
to guarantee that you actually put something on the ring before
updating the state otherwise you can stall the Tx ring without
triggering the watchdog by just hammering this.

> +	for (nxmit = 0; nxmit < n; nxmit++) {
> +		xmit = tsnep_xdp_xmit_frame_ring(xdp[nxmit],
> +						 &adapter->tx[queue],
> +						 TSNEP_TX_TYPE_XDP_NDO);
> +		if (!xmit)
> +			break;

So move txq_trans_cond_update(nq) here.

> +	}
> +
> +	if (flags & XDP_XMIT_FLUSH)
> +		tsnep_xdp_xmit_flush(&adapter->tx[queue]);
> +
> +	__netif_tx_unlock(nq);
> +
> +	return nxmit;
> +}
> +
>  static const struct net_device_ops tsnep_netdev_ops = {
>  	.ndo_open = tsnep_netdev_open,
>  	.ndo_stop = tsnep_netdev_close,
> @@ -1341,6 +1527,7 @@ static const struct net_device_ops tsnep_netdev_ops = {
>  	.ndo_set_features = tsnep_netdev_set_features,
>  	.ndo_get_tstamp = tsnep_netdev_get_tstamp,
>  	.ndo_setup_tc = tsnep_tc_setup,
> +	.ndo_xdp_xmit = tsnep_netdev_xdp_xmit,
>  };
>  
>  static int tsnep_mac_init(struct tsnep_adapter *adapter)

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