[PATCH v2 4/5] net: ethernet: mediatek: enhance RX path by reducing the frequency of the memory barrier used

[Sean Wang]

The patch makes moving wmb() to outside the loop that could help
RX path handling more faster although that RX descriptors aren't
freed for DMA to use as soon as possible, but based on my experiment
and the result show it still can reach about 943Mbpis without
performance drop that is tested based on the setup with one port
using gigaphy and 256 RX descriptors for DMA to move.

Signed-off-by: Sean Wang <sean.wang at mediatek.com>
---
 drivers/net/ethernet/mediatek/mtk_eth_soc.c |   11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
index b782330..53e24c1 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -893,14 +893,15 @@ release_desc:
 		rxd->rxd2 = RX_DMA_PLEN0(ring->buf_size);
 
 		ring->calc_idx = idx;
-		/* make sure that all changes to the dma ring are flushed before
-		 * we continue
-		 */
-		wmb();
-		mtk_w32(eth, ring->calc_idx, MTK_QRX_CRX_IDX0);
 		done++;
 	}
 
+    /* make sure that all changes to the dma ring are flushed before
+     * we continue
+     */
+	wmb();
+	mtk_w32(eth, ring->calc_idx, MTK_QRX_CRX_IDX0);
+
 	if (done < budget)
 		mtk_w32(eth, MTK_RX_DONE_INT, MTK_QMTK_INT_STATUS);
 
-- 
1.7.9.5