[PATCH intel-next 2/5] i40e: avoid per buffer next_to_clean access from i40e_ring

[Tirthendu Sarkar]

Change read/write of next_to_clean from per buffer to beginning and end
of i40_clean_rx_irq(). Use local variables for per buffer increments.

Move out default reading of buffer from 'next_to_clean' in
i40e_get_rx_buffer() and use caller provided index instead. This will
enable walking through all buffers of a multi-buffer packet.

Signed-off-by: Tirthendu Sarkar <tirthendu.sarkar@xxxxxxxxx>
---
 drivers/net/ethernet/intel/i40e/i40e_txrx.c | 33 ++++++++-------------
 1 file changed, 13 insertions(+), 20 deletions(-)

diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
index a7fba294a8f4..c6296cf08294 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
@@ -12,6 +12,7 @@
 #include "i40e_xsk.h"
 
 #define I40E_TXD_CMD (I40E_TX_DESC_CMD_EOP | I40E_TX_DESC_CMD_RS)
+#define I40E_IDX_NEXT(n, max) { if (++(n) > (max)) n = 0; }
 /**
  * i40e_fdir - Generate a Flow Director descriptor based on fdata
  * @tx_ring: Tx ring to send buffer on
@@ -2056,16 +2057,18 @@ static void i40e_add_rx_frag(struct i40e_ring *rx_ring,
  * i40e_get_rx_buffer - Fetch Rx buffer and synchronize data for use
  * @rx_ring: rx descriptor ring to transact packets on
  * @size: size of buffer to add to skb
+ * @next: index of the buffer to be fetched
  *
  * This function will pull an Rx buffer from the ring and synchronize it
  * for use by the CPU.
  */
 static struct i40e_rx_buffer *i40e_get_rx_buffer(struct i40e_ring *rx_ring,
-						 const unsigned int size)
+						 const unsigned int size,
+						 u32 next)
 {
 	struct i40e_rx_buffer *rx_buffer;
 
-	rx_buffer = i40e_rx_bi(rx_ring, rx_ring->next_to_clean);
+	rx_buffer = i40e_rx_bi(rx_ring, next);
 	rx_buffer->page_count =
 #if (PAGE_SIZE < 8192)
 		page_count(rx_buffer->page);
@@ -2402,19 +2405,6 @@ void i40e_finalize_xdp_rx(struct i40e_ring *rx_ring, unsigned int xdp_res)
 	}
 }
 
-/**
- * i40e_inc_ntc: Advance the next_to_clean index
- * @rx_ring: Rx ring
- **/
-static void i40e_inc_ntc(struct i40e_ring *rx_ring)
-{
-	u32 ntc = rx_ring->next_to_clean + 1;
-
-	ntc = (ntc < rx_ring->count) ? ntc : 0;
-	rx_ring->next_to_clean = ntc;
-	prefetch(I40E_RX_DESC(rx_ring, ntc));
-}
-
 /**
  * i40e_clean_rx_irq - Clean completed descriptors from Rx ring - bounce buf
  * @rx_ring: rx descriptor ring to transact packets on
@@ -2435,6 +2425,8 @@ static int i40e_clean_rx_irq(struct i40e_ring *rx_ring, int budget,
 	u16 cleaned_count = I40E_DESC_UNUSED(rx_ring);
 	unsigned int offset = rx_ring->rx_offset;
 	struct sk_buff *skb = rx_ring->skb;
+	u16 ntc = rx_ring->next_to_clean;
+	u16 rmax = rx_ring->count - 1;
 	unsigned int xdp_xmit = 0;
 	struct bpf_prog *xdp_prog;
 	bool failure = false;
@@ -2461,7 +2453,7 @@ static int i40e_clean_rx_irq(struct i40e_ring *rx_ring, int budget,
 			cleaned_count = 0;
 		}
 
-		rx_desc = I40E_RX_DESC(rx_ring, rx_ring->next_to_clean);
+		rx_desc = I40E_RX_DESC(rx_ring, ntc);
 
 		/* status_error_len will always be zero for unused descriptors
 		 * because it's cleared in cleanup, and overlaps with hdr_addr
@@ -2480,8 +2472,8 @@ static int i40e_clean_rx_irq(struct i40e_ring *rx_ring, int budget,
 			i40e_clean_programming_status(rx_ring,
 						      rx_desc->raw.qword[0],
 						      qword);
-			rx_buffer = i40e_rx_bi(rx_ring, rx_ring->next_to_clean);
-			i40e_inc_ntc(rx_ring);
+			rx_buffer = i40e_rx_bi(rx_ring, ntc);
+			I40E_IDX_NEXT(ntc, rmax);
 			i40e_reuse_rx_page(rx_ring, rx_buffer);
 			cleaned_count++;
 			continue;
@@ -2493,7 +2485,7 @@ static int i40e_clean_rx_irq(struct i40e_ring *rx_ring, int budget,
 			break;
 
 		i40e_trace(clean_rx_irq, rx_ring, rx_desc, skb);
-		rx_buffer = i40e_get_rx_buffer(rx_ring, size);
+		rx_buffer = i40e_get_rx_buffer(rx_ring, size, ntc);
 
 		/* retrieve a buffer from the ring */
 		if (!skb) {
@@ -2537,7 +2529,7 @@ static int i40e_clean_rx_irq(struct i40e_ring *rx_ring, int budget,
 		i40e_put_rx_buffer(rx_ring, rx_buffer);
 		cleaned_count++;
 
-		i40e_inc_ntc(rx_ring);
+		I40E_IDX_NEXT(ntc, rmax);
 		if (i40e_is_non_eop(rx_ring, rx_desc))
 			continue;
 
@@ -2559,6 +2551,7 @@ static int i40e_clean_rx_irq(struct i40e_ring *rx_ring, int budget,
 		/* update budget accounting */
 		total_rx_packets++;
 	}
+	rx_ring->next_to_clean = ntc;
 
 	i40e_finalize_xdp_rx(rx_ring, xdp_xmit);
 	rx_ring->skb = skb;
-- 
2.34.1