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

From: Yanteng Si <[email-masked]>
Date: Thu, 16 Jan 2025 00:24:06 +0800

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 <[email-masked]>
> Reviewed-by: Alexander Lobakin <[email-masked]>
Reviewed-by: Yanteng Si <[email-masked]>

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),