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

Matteo Croce
2021-06-09T13:48:22Z

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@microsoft.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