sfc: Enable RX DMA scattering where possible

Enable RX DMA scattering iff an RX buffer large enough for the current
MTU will not fit into a single page and the NIC supports DMA
scattering for kernel-mode RX queues.

On Falcon and Siena, the RX_USR_BUF_SIZE field is used as the DMA
limit for both all RX queues with scatter enabled.  Set it to 1824,
matching what Onload uses now.

Maintain a statistic for frames truncated due to lack of descriptors
(rx_nodesc_trunc).  This is distinct from rx_frm_trunc which may be
incremented when scattering is disabled and implies an over-length
frame.

Whenever an MTU change causes scattering to be turned on or off,
update filters that point to the PF queues, but leave others
unchanged, as VF drivers assume scattering is off.

Add n_frags parameters to various functions, and make them iterate:
- efx_rx_packet()
- efx_recycle_rx_buffers()
- efx_rx_mk_skb()
- efx_rx_deliver()

Make efx_handle_rx_event() responsible for updating
efx_rx_queue::removed_count.

Change the RX pipeline state to a starting ring index and number of
fragments, and make __efx_rx_packet() responsible for clearing it.

Based on earlier versions by David Riddoch and Jon Cooper.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

1 files changed, 138 insertions, 73 deletions

diff --git a/drivers/net/ethernet/sfc/rx.c b/drivers/net/ethernet/sfc/rx.c
index 04518722ac1d..88aa1ff01e3f 100644
--- a/drivers/net/ethernet/sfc/rx.c
+++ b/drivers/net/ethernet/sfc/rx.c
@@ -39,13 +39,17 @@
  */
 static unsigned int rx_refill_threshold;
 
+/* Each packet can consume up to ceil(max_frame_len / buffer_size) buffers */
+#define EFX_RX_MAX_FRAGS DIV_ROUND_UP(EFX_MAX_FRAME_LEN(EFX_MAX_MTU), \
+				      EFX_RX_USR_BUF_SIZE)
+
 /*
  * RX maximum head room required.
  *
- * This must be at least 1 to prevent overflow and at least 2 to allow
- * pipelined receives.
+ * This must be at least 1 to prevent overflow, plus one packet-worth
+ * to allow pipelined receives.
  */
-#define EFX_RXD_HEAD_ROOM 2
+#define EFX_RXD_HEAD_ROOM (1 + EFX_RX_MAX_FRAGS)
 
 static inline u8 *efx_rx_buf_va(struct efx_rx_buffer *buf)
 {
@@ -66,6 +70,15 @@ static inline u32 efx_rx_buf_hash(const u8 *eh)
 #endif
 }
 
+static inline struct efx_rx_buffer *
+efx_rx_buf_next(struct efx_rx_queue *rx_queue, struct efx_rx_buffer *rx_buf)
+{
+	if (unlikely(rx_buf == efx_rx_buffer(rx_queue, rx_queue->ptr_mask)))
+		return efx_rx_buffer(rx_queue, 0);
+	else
+		return rx_buf + 1;
+}
+
 /**
  * efx_init_rx_buffers - create EFX_RX_BATCH page-based RX buffers
  *
@@ -199,28 +212,34 @@ static void efx_resurrect_rx_buffer(struct efx_rx_queue *rx_queue,
 	++rx_queue->added_count;
 }
 
-/* Recycle the given rx buffer directly back into the rx_queue. There is
- * always room to add this buffer, because we've just popped a buffer. */
-static void efx_recycle_rx_buffer(struct efx_channel *channel,
-				  struct efx_rx_buffer *rx_buf)
+/* Recycle buffers directly back into the rx_queue. There is always
+ * room to add these buffer, because we've just popped them.
+ */
+static void efx_recycle_rx_buffers(struct efx_channel *channel,
+				   struct efx_rx_buffer *rx_buf,
+				   unsigned int n_frags)
 {
 	struct efx_nic *efx = channel->efx;
 	struct efx_rx_queue *rx_queue = efx_channel_get_rx_queue(channel);
 	struct efx_rx_buffer *new_buf;
 	unsigned index;
 
-	rx_buf->flags = 0;
+	do {
+		rx_buf->flags = 0;
 
-	if (efx->rx_dma_len <= EFX_RX_HALF_PAGE &&
-	    page_count(rx_buf->page) == 1)
-		efx_resurrect_rx_buffer(rx_queue, rx_buf);
+		if (efx->rx_dma_len <= EFX_RX_HALF_PAGE &&
+		    page_count(rx_buf->page) == 1)
+			efx_resurrect_rx_buffer(rx_queue, rx_buf);
 
-	index = rx_queue->added_count & rx_queue->ptr_mask;
-	new_buf = efx_rx_buffer(rx_queue, index);
+		index = rx_queue->added_count & rx_queue->ptr_mask;
+		new_buf = efx_rx_buffer(rx_queue, index);
 
-	memcpy(new_buf, rx_buf, sizeof(*new_buf));
-	rx_buf->page = NULL;
-	++rx_queue->added_count;
+		memcpy(new_buf, rx_buf, sizeof(*new_buf));
+		rx_buf->page = NULL;
+		++rx_queue->added_count;
+
+		rx_buf = efx_rx_buf_next(rx_queue, rx_buf);
+	} while (--n_frags);
 }
 
 /**
@@ -328,46 +347,56 @@ static void efx_rx_packet__check_len(struct efx_rx_queue *rx_queue,
 /* Pass a received packet up through GRO.  GRO can handle pages
  * regardless of checksum state and skbs with a good checksum.
  */
-static void efx_rx_packet_gro(struct efx_channel *channel,
-			      struct efx_rx_buffer *rx_buf,
-			      const u8 *eh)
+static void
+efx_rx_packet_gro(struct efx_channel *channel, struct efx_rx_buffer *rx_buf,
+		  unsigned int n_frags, u8 *eh)
 {
 	struct napi_struct *napi = &channel->napi_str;
 	gro_result_t gro_result;
 	struct efx_nic *efx = channel->efx;
-	struct page *page = rx_buf->page;
 	struct sk_buff *skb;
 
-	rx_buf->page = NULL;
-
 	skb = napi_get_frags(napi);
-	if (!skb) {
-		put_page(page);
+	if (unlikely(!skb)) {
+		while (n_frags--) {
+			put_page(rx_buf->page);
+			rx_buf->page = NULL;
+			rx_buf = efx_rx_buf_next(&channel->rx_queue, rx_buf);
+		}
 		return;
 	}
 
 	if (efx->net_dev->features & NETIF_F_RXHASH)
 		skb->rxhash = efx_rx_buf_hash(eh);
-
-	skb_fill_page_desc(skb, 0, page, rx_buf->page_offset, rx_buf->len);
-
-	skb->len = rx_buf->len;
-	skb->data_len = rx_buf->len;
-	skb->truesize += rx_buf->len;
 	skb->ip_summed = ((rx_buf->flags & EFX_RX_PKT_CSUMMED) ?
 			  CHECKSUM_UNNECESSARY : CHECKSUM_NONE);
 
-	skb_record_rx_queue(skb, channel->rx_queue.core_index);
+	for (;;) {
+		skb_fill_page_desc(skb, skb_shinfo(skb)->nr_frags,
+				   rx_buf->page, rx_buf->page_offset,
+				   rx_buf->len);
+		rx_buf->page = NULL;
+		skb->len += rx_buf->len;
+		if (skb_shinfo(skb)->nr_frags == n_frags)
+			break;
 
-		gro_result = napi_gro_frags(napi);
+		rx_buf = efx_rx_buf_next(&channel->rx_queue, rx_buf);
+	}
+
+	skb->data_len = skb->len;
+	skb->truesize += n_frags * efx->rx_buffer_truesize;
+
+	skb_record_rx_queue(skb, channel->rx_queue.core_index);
 
+	gro_result = napi_gro_frags(napi);
 	if (gro_result != GRO_DROP)
 		channel->irq_mod_score += 2;
 }
 
-/* Allocate and construct an SKB around a struct page.*/
+/* Allocate and construct an SKB around page fragments */
 static struct sk_buff *efx_rx_mk_skb(struct efx_channel *channel,
 				     struct efx_rx_buffer *rx_buf,
+				     unsigned int n_frags,
 				     u8 *eh, int hdr_len)
 {
 	struct efx_nic *efx = channel->efx;
@@ -381,25 +410,32 @@ static struct sk_buff *efx_rx_mk_skb(struct efx_channel *channel,
 	EFX_BUG_ON_PARANOID(rx_buf->len < hdr_len);
 
 	skb_reserve(skb, EFX_PAGE_SKB_ALIGN);
+	memcpy(__skb_put(skb, hdr_len), eh, hdr_len);
 
-	skb->len = rx_buf->len;
-	skb->truesize = rx_buf->len + sizeof(struct sk_buff);
-	memcpy(skb->data, eh, hdr_len);
-	skb->tail += hdr_len;
-
-	/* Append the remaining page onto the frag list */
+	/* Append the remaining page(s) onto the frag list */
 	if (rx_buf->len > hdr_len) {
-		skb->data_len = skb->len - hdr_len;
-		skb_fill_page_desc(skb, 0, rx_buf->page,
-				   rx_buf->page_offset + hdr_len,
-				   skb->data_len);
+		rx_buf->page_offset += hdr_len;
+		rx_buf->len -= hdr_len;
+
+		for (;;) {
+			skb_fill_page_desc(skb, skb_shinfo(skb)->nr_frags,
+					   rx_buf->page, rx_buf->page_offset,
+					   rx_buf->len);
+			rx_buf->page = NULL;
+			skb->len += rx_buf->len;
+			skb->data_len += rx_buf->len;
+			if (skb_shinfo(skb)->nr_frags == n_frags)
+				break;
+
+			rx_buf = efx_rx_buf_next(&channel->rx_queue, rx_buf);
+		}
 	} else {
 		__free_pages(rx_buf->page, efx->rx_buffer_order);
-		skb->data_len = 0;
+		rx_buf->page = NULL;
+		n_frags = 0;
 	}
 
-	/* Ownership has transferred from the rx_buf to skb */
-	rx_buf->page = NULL;
+	skb->truesize += n_frags * efx->rx_buffer_truesize;
 
 	/* Move past the ethernet header */
 	skb->protocol = eth_type_trans(skb, efx->net_dev);
@@ -408,7 +444,7 @@ static struct sk_buff *efx_rx_mk_skb(struct efx_channel *channel,
 }
 
 void efx_rx_packet(struct efx_rx_queue *rx_queue, unsigned int index,
-		   unsigned int len, u16 flags)
+		   unsigned int n_frags, unsigned int len, u16 flags)
 {
 	struct efx_nic *efx = rx_queue->efx;
 	struct efx_channel *channel = efx_rx_queue_channel(rx_queue);
@@ -417,35 +453,43 @@ void efx_rx_packet(struct efx_rx_queue *rx_queue, unsigned int index,
 	rx_buf = efx_rx_buffer(rx_queue, index);
 	rx_buf->flags |= flags;
 
-	/* This allows the refill path to post another buffer.
-	 * EFX_RXD_HEAD_ROOM ensures that the slot we are using
-	 * isn't overwritten yet.
-	 */
-	rx_queue->removed_count++;
-
-	/* Validate the length encoded in the event vs the descriptor pushed */
-	efx_rx_packet__check_len(rx_queue, rx_buf, len);
+	/* Validate the number of fragments and completed length */
+	if (n_frags == 1) {
+		efx_rx_packet__check_len(rx_queue, rx_buf, len);
+	} else if (unlikely(n_frags > EFX_RX_MAX_FRAGS) ||
+		   unlikely(len <= (n_frags - 1) * EFX_RX_USR_BUF_SIZE) ||
+		   unlikely(len > n_frags * EFX_RX_USR_BUF_SIZE) ||
+		   unlikely(!efx->rx_scatter)) {
+		/* If this isn't an explicit discard request, either
+		 * the hardware or the driver is broken.
+		 */
+		WARN_ON(!(len == 0 && rx_buf->flags & EFX_RX_PKT_DISCARD));
+		rx_buf->flags |= EFX_RX_PKT_DISCARD;
+	}
 
 	netif_vdbg(efx, rx_status, efx->net_dev,
-		   "RX queue %d received id %x at %llx+%x %s%s\n",
+		   "RX queue %d received ids %x-%x len %d %s%s\n",
 		   efx_rx_queue_index(rx_queue), index,
-		   (unsigned long long)rx_buf->dma_addr, len,
+		   (index + n_frags - 1) & rx_queue->ptr_mask, len,
 		   (rx_buf->flags & EFX_RX_PKT_CSUMMED) ? " [SUMMED]" : "",
 		   (rx_buf->flags & EFX_RX_PKT_DISCARD) ? " [DISCARD]" : "");
 
-	/* Discard packet, if instructed to do so */
+	/* Discard packet, if instructed to do so.  Process the
+	 * previous receive first.
+	 */
 	if (unlikely(rx_buf->flags & EFX_RX_PKT_DISCARD)) {
-		efx_recycle_rx_buffer(channel, rx_buf);
-
-		/* Don't hold off the previous receive */
-		rx_buf = NULL;
-		goto out;
+		efx_rx_flush_packet(channel);
+		efx_recycle_rx_buffers(channel, rx_buf, n_frags);
+		return;
 	}
 
+	if (n_frags == 1)
+		rx_buf->len = len;
+
 	/* Release and/or sync DMA mapping - assumes all RX buffers
 	 * consumed in-order per RX queue
 	 */
-	efx_unmap_rx_buffer(efx, rx_buf, len);
+	efx_unmap_rx_buffer(efx, rx_buf, rx_buf->len);
 
 	/* Prefetch nice and early so data will (hopefully) be in cache by
 	 * the time we look at it.
@@ -453,23 +497,40 @@ void efx_rx_packet(struct efx_rx_queue *rx_queue, unsigned int index,
 	prefetch(efx_rx_buf_va(rx_buf));
 
 	rx_buf->page_offset += efx->type->rx_buffer_hash_size;
-	rx_buf->len = len - efx->type->rx_buffer_hash_size;
+	rx_buf->len -= efx->type->rx_buffer_hash_size;
+
+	if (n_frags > 1) {
+		/* Release/sync DMA mapping for additional fragments.
+		 * Fix length for last fragment.
+		 */
+		unsigned int tail_frags = n_frags - 1;
+
+		for (;;) {
+			rx_buf = efx_rx_buf_next(rx_queue, rx_buf);
+			if (--tail_frags == 0)
+				break;
+			efx_unmap_rx_buffer(efx, rx_buf, EFX_RX_USR_BUF_SIZE);
+		}
+		rx_buf->len = len - (n_frags - 1) * EFX_RX_USR_BUF_SIZE;
+		efx_unmap_rx_buffer(efx, rx_buf, rx_buf->len);
+	}
 
 	/* Pipeline receives so that we give time for packet headers to be
 	 * prefetched into cache.
 	 */
-out:
 	efx_rx_flush_packet(channel);
-	channel->rx_pkt = rx_buf;
+	channel->rx_pkt_n_frags = n_frags;
+	channel->rx_pkt_index = index;
 }
 
 static void efx_rx_deliver(struct efx_channel *channel, u8 *eh,
-			   struct efx_rx_buffer *rx_buf)
+			   struct efx_rx_buffer *rx_buf,
+			   unsigned int n_frags)
 {
 	struct sk_buff *skb;
 	u16 hdr_len = min_t(u16, rx_buf->len, EFX_SKB_HEADERS);
 
-	skb = efx_rx_mk_skb(channel, rx_buf, eh, hdr_len);
+	skb = efx_rx_mk_skb(channel, rx_buf, n_frags, eh, hdr_len);
 	if (unlikely(skb == NULL)) {
 		efx_free_rx_buffer(channel->efx, rx_buf);
 		return;
@@ -488,9 +549,11 @@ static void efx_rx_deliver(struct efx_channel *channel, u8 *eh,
 }
 
 /* Handle a received packet.  Second half: Touches packet payload. */
-void __efx_rx_packet(struct efx_channel *channel, struct efx_rx_buffer *rx_buf)
+void __efx_rx_packet(struct efx_channel *channel)
 {
 	struct efx_nic *efx = channel->efx;
+	struct efx_rx_buffer *rx_buf =
+		efx_rx_buffer(&channel->rx_queue, channel->rx_pkt_index);
 	u8 *eh = efx_rx_buf_va(rx_buf);
 
 	/* If we're in loopback test, then pass the packet directly to the
@@ -499,16 +562,18 @@ void __efx_rx_packet(struct efx_channel *channel, struct efx_rx_buffer *rx_buf)
 	if (unlikely(efx->loopback_selftest)) {
 		efx_loopback_rx_packet(efx, eh, rx_buf->len);
 		efx_free_rx_buffer(efx, rx_buf);
-		return;
+		goto out;
 	}
 
 	if (unlikely(!(efx->net_dev->features & NETIF_F_RXCSUM)))
 		rx_buf->flags &= ~EFX_RX_PKT_CSUMMED;
 
 	if (!channel->type->receive_skb)
-		efx_rx_packet_gro(channel, rx_buf, eh);
+		efx_rx_packet_gro(channel, rx_buf, channel->rx_pkt_n_frags, eh);
 	else
-		efx_rx_deliver(channel, eh, rx_buf);
+		efx_rx_deliver(channel, eh, rx_buf, channel->rx_pkt_n_frags);
+out:
+	channel->rx_pkt_n_frags = 0;
 }
 
 int efx_probe_rx_queue(struct efx_rx_queue *rx_queue)