[PATCH net-next] net: mvneta: avoid possible cache misses in mvneta_rx_swbm

[Lorenzo Bianconi]

Do not use rx_desc pointers if possible since rx descriptors are stored in
uncached memory and dereferencing rx_desc pointers generate extra loads.
This patch improves XDP_DROP performance of ~ 110Kpps (700Kpps vs 590Kpps)
on Marvell Espressobin

Analyzed-by: Ilias Apalodimas <ilias.apalodi...@linaro.org>
Signed-off-by: Lorenzo Bianconi <lore...@kernel.org>
---
 drivers/net/ethernet/marvell/mvneta.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/marvell/mvneta.c 
b/drivers/net/ethernet/marvell/mvneta.c
index bb485745b72a..d095718355d3 100644
--- a/drivers/net/ethernet/marvell/mvneta.c
+++ b/drivers/net/ethernet/marvell/mvneta.c
@@ -2236,19 +2236,22 @@ mvneta_swbm_rx_frame(struct mvneta_port *pp,
        enum dma_data_direction dma_dir;
        struct skb_shared_info *sinfo;
 
-       if (rx_desc->data_size > MVNETA_MAX_RX_BUF_SIZE) {
+       if (*size > MVNETA_MAX_RX_BUF_SIZE) {
                len = MVNETA_MAX_RX_BUF_SIZE;
                data_len += len;
        } else {
-               len = rx_desc->data_size;
+               len = *size;
                data_len += len - ETH_FCS_LEN;
        }
+       *size = *size - len;
 
        dma_dir = page_pool_get_dma_dir(rxq->page_pool);
        dma_sync_single_for_cpu(dev->dev.parent,
                                rx_desc->buf_phys_addr,
                                len, dma_dir);
 
+       rx_desc->buf_phys_addr = 0;
+
        /* Prefetch header */
        prefetch(data);
 
@@ -2259,9 +2262,6 @@ mvneta_swbm_rx_frame(struct mvneta_port *pp,
 
        sinfo = xdp_get_shared_info_from_buff(xdp);
        sinfo->nr_frags = 0;
-
-       *size = rx_desc->data_size - len;
-       rx_desc->buf_phys_addr = 0;
 }
 
 static void
@@ -2375,7 +2375,7 @@ static int mvneta_rx_swbm(struct napi_struct *napi,
 
                        size = rx_desc->data_size;
                        frame_sz = size - ETH_FCS_LEN;
-                       desc_status = rx_desc->status;
+                       desc_status = rx_status;
 
                        mvneta_swbm_rx_frame(pp, rx_desc, rxq, &xdp_buf,
                                             &size, page);
-- 
2.26.2