Re: [PATCH net-next v3 3/4] net: stmmac: Optimize cache prefetch in RX path

Yanteng Si
2025-01-15T16:24:49Z

在 1/15/25 11:27, Furong Xu 写道:
> Current code prefetches cache lines for the received frame first, and
> then dma_sync_single_for_cpu() against this frame, this is wrong.
> Cache prefetch should be triggered after dma_sync_single_for_cpu().
>
> This patch brings ~2.8% driver performance improvement in a TCP RX
> throughput test with iPerf tool on a single isolated Cortex-A65 CPU
> core, 2.84 Gbits/sec increased to 2.92 Gbits/sec.
>
> Signed-off-by: Furong Xu <0x1207@gmail.com>
> Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Reviewed-by: Yanteng Si <si.yanteng@linux.dev>

Thanks,
Yanteng
> ---
> drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 5 +----
> 1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index 811e2d372abf..ad928e8e21a9 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -5508,10 +5508,6 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
>
> /* Buffer is good. Go on. */
>
> - prefetch(page_address(buf->page) + buf->page_offset);
> - if (buf->sec_page)
> - prefetch(page_address(buf->sec_page));
> -
> buf1_len = stmmac_rx_buf1_len(priv, p, status, len);
> len += buf1_len;
> buf2_len = stmmac_rx_buf2_len(priv, p, status, len);
> @@ -5533,6 +5529,7 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
>
> dma_sync_single_for_cpu(priv->device, buf->addr,
> buf1_len, dma_dir);
> + prefetch(page_address(buf->page) + buf->page_offset);
>
> xdp_init_buff(&ctx.xdp, buf_sz, &rx_q->xdp_rxq);
> xdp_prepare_buff(&ctx.xdp, page_address(buf->page),