iavf: drop page splitting and recycling

As an intermediate step, remove all page splitting/recycling code. Just
always allocate a new page and don't touch its refcount, so that it gets
freed by the core stack later.
Same for the "in-place" recycling, i.e. when an unused buffer gets
assigned to a first needs-refilling descriptor. In some cases, this
was leading to moving up to 63 &iavf_rx_buf structures around the ring
on a per-field basis -- not something wanted on hotpath.
The change allows to greatly simplify certain parts of the code:

Function: add/remove: 0/2 grow/shrink: 0/7 up/down: 0/-744 (-744)

Although the array of &iavf_rx_buf is barely used now and could be
replaced with just page pointer array, don't touch it now to not
complicate replacing it with libie Rx buffer struct later on.
No surprise perf loses up to 30% here, but that regression will
go away once PP lands.
Note that iavf_rx_pg_*() definitions are left to reduce diffstat.
They will be removed with the conversion to Page Pool.

Signed-off-by: Alexander Lobakin <[email protected]>
Signed-off-by: Tony Nguyen <[email protected]>

Author: alobakin

drivers/net/ethernet/intel/iavf/iavf_main.c

@@ -715,32 +715,10 @@ static void iavf_configure_tx(struct iavf_adapter *adapter)
  **/
 static void iavf_configure_rx(struct iavf_adapter *adapter)
 {
-	unsigned int rx_buf_len = IAVF_RXBUFFER_2048;
 	struct iavf_hw *hw = &adapter->hw;
-	int i;
-
-	if (PAGE_SIZE < 8192) {
-		struct net_device *netdev = adapter->netdev;
 
-		/* For jumbo frames on systems with 4K pages we have to use
-		 * an order 1 page, so we might as well increase the size
-		 * of our Rx buffer to make better use of the available space
-		 */
-		rx_buf_len = IAVF_RXBUFFER_3072;
-
-		/* We use a 1536 buffer size for configurations with
-		 * standard Ethernet mtu.  On x86 this gives us enough room
-		 * for shared info and 192 bytes of padding.
-		 */
-		if (!IAVF_2K_TOO_SMALL_WITH_PADDING &&
-		    (netdev->mtu <= ETH_DATA_LEN))
-			rx_buf_len = IAVF_RXBUFFER_1536 - NET_IP_ALIGN;
-	}
-
-	for (i = 0; i < adapter->num_active_queues; i++) {
+	for (u32 i = 0; i < adapter->num_active_queues; i++)
 		adapter->rx_rings[i].tail = hw->hw_addr + IAVF_QRX_TAIL1(i);
-		adapter->rx_rings[i].rx_buf_len = rx_buf_len;
-	}
 }
 
 /**

drivers/net/ethernet/intel/iavf/iavf_txrx.c

@@ -715,7 +715,7 @@ static void iavf_clean_rx_ring(struct iavf_ring *rx_ring)
 		dma_sync_single_range_for_cpu(rx_ring->dev,
 					      rx_bi->dma,
 					      rx_bi->page_offset,
-					      rx_ring->rx_buf_len,
+					      IAVF_RXBUFFER_3072,
 					      DMA_FROM_DEVICE);
 
 		/* free resources associated with mapping */
@@ -724,7 +724,7 @@ static void iavf_clean_rx_ring(struct iavf_ring *rx_ring)
 				     DMA_FROM_DEVICE,
 				     IAVF_RX_DMA_ATTR);
 
-		__page_frag_cache_drain(rx_bi->page, rx_bi->pagecnt_bias);
+		__free_page(rx_bi->page);
 
 		rx_bi->page = NULL;
 		rx_bi->page_offset = 0;
@@ -736,7 +736,6 @@ static void iavf_clean_rx_ring(struct iavf_ring *rx_ring)
 	/* Zero out the descriptor ring */
 	memset(rx_ring->desc, 0, rx_ring->size);
 
-	rx_ring->next_to_alloc = 0;
 	rx_ring->next_to_clean = 0;
 	rx_ring->next_to_use = 0;
 }
@@ -792,7 +791,6 @@ int iavf_setup_rx_descriptors(struct iavf_ring *rx_ring)
 		goto err;
 	}
 
-	rx_ring->next_to_alloc = 0;
 	rx_ring->next_to_clean = 0;
 	rx_ring->next_to_use = 0;
 
@@ -812,9 +810,6 @@ static void iavf_release_rx_desc(struct iavf_ring *rx_ring, u32 val)
 {
 	rx_ring->next_to_use = val;
 
-	/* update next to alloc since we have filled the ring */
-	rx_ring->next_to_alloc = val;
-
 	/* Force memory writes to complete before letting h/w
 	 * know there are new descriptors to fetch.  (Only
 	 * applicable for weak-ordered memory model archs,
@@ -838,12 +833,6 @@ static bool iavf_alloc_mapped_page(struct iavf_ring *rx_ring,
 	struct page *page = bi->page;
 	dma_addr_t dma;
 
-	/* since we are recycling buffers we should seldom need to alloc */
-	if (likely(page)) {
-		rx_ring->rx_stats.page_reuse_count++;
-		return true;
-	}
-
 	/* alloc new page for storage */
 	page = dev_alloc_pages(iavf_rx_pg_order(rx_ring));
 	if (unlikely(!page)) {
@@ -870,9 +859,6 @@ static bool iavf_alloc_mapped_page(struct iavf_ring *rx_ring,
 	bi->page = page;
 	bi->page_offset = IAVF_SKB_PAD;
 
-	/* initialize pagecnt_bias to 1 representing we fully own page */
-	bi->pagecnt_bias = 1;
-
 	return true;
 }
 
@@ -924,7 +910,7 @@ bool iavf_alloc_rx_buffers(struct iavf_ring *rx_ring, u16 cleaned_count)
 		/* sync the buffer for use by the device */
 		dma_sync_single_range_for_device(rx_ring->dev, bi->dma,
 						 bi->page_offset,
-						 rx_ring->rx_buf_len,
+						 IAVF_RXBUFFER_3072,
 						 DMA_FROM_DEVICE);
 
 		/* Refresh the desc even if buffer_addrs didn't change
@@ -1102,91 +1088,6 @@ static bool iavf_cleanup_headers(struct iavf_ring *rx_ring, struct sk_buff *skb)
 	return false;
 }
 
-/**
- * iavf_reuse_rx_page - page flip buffer and store it back on the ring
- * @rx_ring: rx descriptor ring to store buffers on
- * @old_buff: donor buffer to have page reused
- *
- * Synchronizes page for reuse by the adapter
- **/
-static void iavf_reuse_rx_page(struct iavf_ring *rx_ring,
-			       struct iavf_rx_buffer *old_buff)
-{
-	struct iavf_rx_buffer *new_buff;
-	u16 nta = rx_ring->next_to_alloc;
-
-	new_buff = &rx_ring->rx_bi[nta];
-
-	/* update, and store next to alloc */
-	nta++;
-	rx_ring->next_to_alloc = (nta < rx_ring->count) ? nta : 0;
-
-	/* transfer page from old buffer to new buffer */
-	new_buff->dma		= old_buff->dma;
-	new_buff->page		= old_buff->page;
-	new_buff->page_offset	= old_buff->page_offset;
-	new_buff->pagecnt_bias	= old_buff->pagecnt_bias;
-}
-
-/**
- * iavf_can_reuse_rx_page - Determine if this page can be reused by
- * the adapter for another receive
- *
- * @rx_buffer: buffer containing the page
- *
- * If page is reusable, rx_buffer->page_offset is adjusted to point to
- * an unused region in the page.
- *
- * For small pages, @truesize will be a constant value, half the size
- * of the memory at page.  We'll attempt to alternate between high and
- * low halves of the page, with one half ready for use by the hardware
- * and the other half being consumed by the stack.  We use the page
- * ref count to determine whether the stack has finished consuming the
- * portion of this page that was passed up with a previous packet.  If
- * the page ref count is >1, we'll assume the "other" half page is
- * still busy, and this page cannot be reused.
- *
- * For larger pages, @truesize will be the actual space used by the
- * received packet (adjusted upward to an even multiple of the cache
- * line size).  This will advance through the page by the amount
- * actually consumed by the received packets while there is still
- * space for a buffer.  Each region of larger pages will be used at
- * most once, after which the page will not be reused.
- *
- * In either case, if the page is reusable its refcount is increased.
- **/
-static bool iavf_can_reuse_rx_page(struct iavf_rx_buffer *rx_buffer)
-{
-	unsigned int pagecnt_bias = rx_buffer->pagecnt_bias;
-	struct page *page = rx_buffer->page;
-
-	/* Is any reuse possible? */
-	if (!dev_page_is_reusable(page))
-		return false;
-
-#if (PAGE_SIZE < 8192)
-	/* if we are only owner of page we can reuse it */
-	if (unlikely((page_count(page) - pagecnt_bias) > 1))
-		return false;
-#else
-#define IAVF_LAST_OFFSET \
-	(SKB_WITH_OVERHEAD(PAGE_SIZE) - IAVF_RXBUFFER_2048)
-	if (rx_buffer->page_offset > IAVF_LAST_OFFSET)
-		return false;
-#endif
-
-	/* If we have drained the page fragment pool we need to update
-	 * the pagecnt_bias and page count so that we fully restock the
-	 * number of references the driver holds.
-	 */
-	if (unlikely(!pagecnt_bias)) {
-		page_ref_add(page, USHRT_MAX);
-		rx_buffer->pagecnt_bias = USHRT_MAX;
-	}
-
-	return true;
-}
-
 /**
  * iavf_add_rx_frag - Add contents of Rx buffer to sk_buff
  * @rx_ring: rx descriptor ring to transact packets on
@@ -1204,24 +1105,13 @@ static void iavf_add_rx_frag(struct iavf_ring *rx_ring,
 			     struct sk_buff *skb,
 			     unsigned int size)
 {
-#if (PAGE_SIZE < 8192)
-	unsigned int truesize = iavf_rx_pg_size(rx_ring) / 2;
-#else
 	unsigned int truesize = SKB_DATA_ALIGN(size + IAVF_SKB_PAD);
-#endif
 
 	if (!size)
 		return;
 
 	skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags, rx_buffer->page,
 			rx_buffer->page_offset, size, truesize);
-
-	/* page is being used so we must update the page offset */
-#if (PAGE_SIZE < 8192)
-	rx_buffer->page_offset ^= truesize;
-#else
-	rx_buffer->page_offset += truesize;
-#endif
 }
 
 /**
@@ -1249,9 +1139,6 @@ static struct iavf_rx_buffer *iavf_get_rx_buffer(struct iavf_ring *rx_ring,
 				      size,
 				      DMA_FROM_DEVICE);
 
-	/* We have pulled a buffer for use, so decrement pagecnt_bias */
-	rx_buffer->pagecnt_bias--;
-
 	return rx_buffer;
 }
 
@@ -1269,12 +1156,8 @@ static struct sk_buff *iavf_build_skb(struct iavf_ring *rx_ring,
 				      unsigned int size)
 {
 	void *va;
-#if (PAGE_SIZE < 8192)
-	unsigned int truesize = iavf_rx_pg_size(rx_ring) / 2;
-#else
 	unsigned int truesize = SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) +
 				SKB_DATA_ALIGN(IAVF_SKB_PAD + size);
-#endif
 	struct sk_buff *skb;
 
 	if (!rx_buffer || !size)
@@ -1292,42 +1175,25 @@ static struct sk_buff *iavf_build_skb(struct iavf_ring *rx_ring,
 	skb_reserve(skb, IAVF_SKB_PAD);
 	__skb_put(skb, size);
 
-	/* buffer is used by skb, update page_offset */
-#if (PAGE_SIZE < 8192)
-	rx_buffer->page_offset ^= truesize;
-#else
-	rx_buffer->page_offset += truesize;
-#endif
-
 	return skb;
 }
 
 /**
- * iavf_put_rx_buffer - Clean up used buffer and either recycle or free
+ * iavf_put_rx_buffer - Unmap used buffer
  * @rx_ring: rx descriptor ring to transact packets on
  * @rx_buffer: rx buffer to pull data from
  *
- * This function will clean up the contents of the rx_buffer.  It will
- * either recycle the buffer or unmap it and free the associated resources.
+ * This function will unmap the buffer after it's written by HW.
  */
 static void iavf_put_rx_buffer(struct iavf_ring *rx_ring,
 			       struct iavf_rx_buffer *rx_buffer)
 {
 	if (!rx_buffer)
 		return;
 
-	if (iavf_can_reuse_rx_page(rx_buffer)) {
-		/* hand second half of page back to the ring */
-		iavf_reuse_rx_page(rx_ring, rx_buffer);
-		rx_ring->rx_stats.page_reuse_count++;
-	} else {
-		/* we are not reusing the buffer so unmap it */
-		dma_unmap_page_attrs(rx_ring->dev, rx_buffer->dma,
-				     iavf_rx_pg_size(rx_ring),
-				     DMA_FROM_DEVICE, IAVF_RX_DMA_ATTR);
-		__page_frag_cache_drain(rx_buffer->page,
-					rx_buffer->pagecnt_bias);
-	}
+	/* we are not reusing the buffer so unmap it */
+	dma_unmap_page_attrs(rx_ring->dev, rx_buffer->dma, PAGE_SIZE,
+			     DMA_FROM_DEVICE, IAVF_RX_DMA_ATTR);
 
 	/* clear contents of buffer_info */
 	rx_buffer->page = NULL;
@@ -1432,8 +1298,6 @@ static int iavf_clean_rx_irq(struct iavf_ring *rx_ring, int budget)
 		/* exit if we failed to retrieve a buffer */
 		if (!skb) {
 			rx_ring->rx_stats.alloc_buff_failed++;
-			if (rx_buffer && size)
-				rx_buffer->pagecnt_bias++;
 			break;
 		}