netdev - [PATCH net-next 15/18] gve: Prefetch packet pages and packet descriptors.

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Message-Id: <20200818194417.2003932-16-awogbemila@google.com>
Date:   Tue, 18 Aug 2020 12:44:14 -0700
From:   David Awogbemila <awogbemila@...gle.com>
To:     netdev@...r.kernel.org
Cc:     Yangchun Fu <yangchun@...gle.com>, Nathan Lewis <npl@...gle.com>,
        David Awogbemila <awogbemila@...gle.com>
Subject: [PATCH net-next 15/18] gve: Prefetch packet pages and packet descriptors.

From: Yangchun Fu <yangchun@...gle.com>

Prefetching appears to help performance.

Signed-off-by: Yangchun Fu <yangchun@...gle.com>
Signed-off-by: Nathan Lewis <npl@...gle.com>
Signed-off-by: David Awogbemila <awogbemila@...gle.com>
---
 drivers/net/ethernet/google/gve/gve_rx.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/net/ethernet/google/gve/gve_rx.c b/drivers/net/ethernet/google/gve/gve_rx.c
index c65615b9e602..24bd556f488e 100644
--- a/drivers/net/ethernet/google/gve/gve_rx.c
+++ b/drivers/net/ethernet/google/gve/gve_rx.c
@@ -447,8 +447,18 @@ static bool gve_rx(struct gve_rx_ring *rx, struct gve_rx_desc *rx_desc,
 	struct gve_rx_data_slot *data_slot;
 	struct sk_buff *skb = NULL;
 	dma_addr_t page_bus;
+	void *va;
 	u16 len;
 
+	/* Prefetch two packet pages ahead, we will need it soon. */
+	page_info = &rx->data.page_info[(idx + 2) & rx->mask];
+	va = page_info->page_address + GVE_RX_PAD +
+			page_info->page_offset;
+
+	prefetch(page_info->page); // Kernel page struct.
+	prefetch(va);              // Packet header.
+	prefetch(va + 64);           // Next cacheline too.
+
 	/* drop this packet */
 	if (unlikely(rx_desc->flags_seq & GVE_RXF_ERR)) {
 		u64_stats_update_begin(&rx->statss);
@@ -618,6 +628,10 @@ bool gve_clean_rx_done(struct gve_rx_ring *rx, int budget,
 			   "[%d] seqno=%d rx->desc.seqno=%d\n",
 			   rx->q_num, GVE_SEQNO(desc->flags_seq),
 			   rx->desc.seqno);
+
+		// prefetch two descriptors ahead
+		prefetch(rx->desc.desc_ring + ((cnt + 2) & rx->mask));
+
 		dropped = !gve_rx(rx, desc, feat, idx);
 		if (!dropped) {
 			bytes += be16_to_cpu(desc->len) - GVE_RX_PAD;
-- 
2.28.0.220.ged08abb693-goog