linux-kernel - [PATCH net-next 2/2] mvpp2: prefetch page

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Date:   Wed,  9 Jun 2021 15:47:14 +0200
From:   Matteo Croce <mcroce@...ux.microsoft.com>
To:     netdev@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Marcin Wojtas <mw@...ihalf.com>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Sven Auhagen <sven.auhagen@...eatech.de>
Subject: [PATCH net-next 2/2] mvpp2: prefetch page

From: Matteo Croce <mcroce@...rosoft.com>

Most of the time during the RX is caused by the compound_head() call
done at the end of the RX loop:

       │     build_skb():
       [...]
       │     static inline struct page *compound_head(struct page *page)
       │     {
       │     unsigned long head = READ_ONCE(page->compound_head);
 65.23 │       ldr  x2, [x1, #8]

Prefetch the page struct as soon as possible, to speedup the RX path
noticeabily by a ~3-4% packet rate in a drop test.

       │     build_skb():
       [...]
       │     static inline struct page *compound_head(struct page *page)
       │     {
       │     unsigned long head = READ_ONCE(page->compound_head);
 17.92 │       ldr  x2, [x1, #8]

Signed-off-by: Matteo Croce <mcroce@...rosoft.com>
---
 drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
index 07d8f3e31b52..9bca8c8f9f8d 100644
--- a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
+++ b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
@@ -3900,15 +3900,19 @@ static int mvpp2_rx(struct mvpp2_port *port, struct napi_struct *napi,
 		phys_addr_t phys_addr;
 		u32 rx_status, timestamp;
 		int pool, rx_bytes, err, ret;
+		struct page *page;
 		void *data;
 
+		phys_addr = mvpp2_rxdesc_cookie_get(port, rx_desc);
+		data = (void *)phys_to_virt(phys_addr);
+		page = virt_to_page(data);
+		prefetch(page);
+
 		rx_done++;
 		rx_status = mvpp2_rxdesc_status_get(port, rx_desc);
 		rx_bytes = mvpp2_rxdesc_size_get(port, rx_desc);
 		rx_bytes -= MVPP2_MH_SIZE;
 		dma_addr = mvpp2_rxdesc_dma_addr_get(port, rx_desc);
-		phys_addr = mvpp2_rxdesc_cookie_get(port, rx_desc);
-		data = (void *)phys_to_virt(phys_addr);
 
 		pool = (rx_status & MVPP2_RXD_BM_POOL_ID_MASK) >>
 			MVPP2_RXD_BM_POOL_ID_OFFS;
@@ -3997,7 +4001,7 @@ static int mvpp2_rx(struct mvpp2_port *port, struct napi_struct *napi,
 		}
 
 		if (pp)
-			skb_mark_for_recycle(skb, virt_to_page(data), pp);
+			skb_mark_for_recycle(skb, page, pp);
 		else
 			dma_unmap_single_attrs(dev->dev.parent, dma_addr,
 					       bm_pool->buf_size, DMA_FROM_DEVICE,
-- 
2.31.1