igb: Only DMA sync frame length

On some platforms, syncing a buffer for DMA is expensive. Rather than
sync the whole 2K receive buffer, only synchronise the length of the
frame, which will typically be the MTU, or a much smaller TCP ACK.

For an IMX6Q, this gives around 6% increased TCP receive performance,
which is cache operations bound and reduces CPU load for TCP transmit.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

1 files changed, 4 insertions, 3 deletions

diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
index a15f82600802..9bcba42abb91 100644
--- a/drivers/net/ethernet/intel/igb/igb_main.c
+++ b/drivers/net/ethernet/intel/igb/igb_main.c
@@ -6856,12 +6856,12 @@ static bool igb_can_reuse_rx_page(struct igb_rx_buffer *rx_buffer,
  **/
 static bool igb_add_rx_frag(struct igb_ring *rx_ring,
                             struct igb_rx_buffer *rx_buffer,
+                            unsigned int size,
                             union e1000_adv_rx_desc *rx_desc,
                             struct sk_buff *skb)
 {
         struct page *page = rx_buffer->page;
         unsigned char *va = page_address(page) + rx_buffer->page_offset;
-        unsigned int size = le16_to_cpu(rx_desc->wb.upper.length);
 #if (PAGE_SIZE < 8192)
         unsigned int truesize = IGB_RX_BUFSZ;
 #else
@@ -6913,6 +6913,7 @@ static struct sk_buff *igb_fetch_rx_buffer(struct igb_ring *rx_ring,
                                            union e1000_adv_rx_desc *rx_desc,
                                            struct sk_buff *skb)
 {
+        unsigned int size = le16_to_cpu(rx_desc->wb.upper.length);
         struct igb_rx_buffer *rx_buffer;
         struct page *page;
 
@@ -6948,11 +6949,11 @@ static struct sk_buff *igb_fetch_rx_buffer(struct igb_ring *rx_ring,
         dma_sync_single_range_for_cpu(rx_ring->dev,
                                       rx_buffer->dma,
                                       rx_buffer->page_offset,
-                                      IGB_RX_BUFSZ,
+                                      size,
                                       DMA_FROM_DEVICE);
 
         /* pull page into skb */
-        if (igb_add_rx_frag(rx_ring, rx_buffer, rx_desc, skb)) {
+        if (igb_add_rx_frag(rx_ring, rx_buffer, size, rx_desc, skb)) {
                 /* hand second half of page back to the ring */
                 igb_reuse_rx_page(rx_ring, rx_buffer);
         } else {