Re: [PATCH net-next RFC] net: ethernet: mtk_eth_soc: use prefetch methods

[Joe Damato <jdamato@fastly.com>]

On Sat, Jul 20, 2024 at 07:46:18PM +0300, Elad Yifee wrote:
> Utilize kernel prefetch methods for faster cache line access.
> This change boosts driver performance,
> allowing the CPU to handle about 5% more packets/sec.

Nit: It'd be great to see before/after numbers and/or an explanation of
how you measured this in the commit message.

> Signed-off-by: Elad Yifee <eladwf@gmail.com>
> ---
>  drivers/net/ethernet/mediatek/mtk_eth_soc.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> index 0cc2dd85652f..1a0704166103 100644
> --- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> +++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> @@ -1963,6 +1963,7 @@ static u32 mtk_xdp_run(struct mtk_eth *eth, struct mtk_rx_ring *ring,
>  	if (!prog)
>  		goto out;
>  
> +	prefetchw(xdp->data_hard_start);

Is there any reason to mix net_prefetch (as you have below) with
prefetch and prefetchw ?

IMHO: you should consider using net_prefetch and net_prefetchw
everywhere instead of using both in your code.

>  	act = bpf_prog_run_xdp(prog, xdp);
>  	switch (act) {
>  	case XDP_PASS:
> @@ -2039,7 +2040,7 @@ static int mtk_poll_rx(struct napi_struct *napi, int budget,
>  		idx = NEXT_DESP_IDX(ring->calc_idx, ring->dma_size);
>  		rxd = ring->dma + idx * eth->soc->rx.desc_size;
>  		data = ring->data[idx];
> -
> +		prefetch(rxd);

Maybe net_prefetch instead, as mentioned above?

>  		if (!mtk_rx_get_desc(eth, &trxd, rxd))
>  			break;
>  
> @@ -2105,6 +2106,7 @@ static int mtk_poll_rx(struct napi_struct *napi, int budget,
>  			if (ret != XDP_PASS)
>  				goto skip_rx;
>  
> +			net_prefetch(xdp.data_meta);
>  			skb = build_skb(data, PAGE_SIZE);
>  			if (unlikely(!skb)) {
>  				page_pool_put_full_page(ring->page_pool,
> @@ -2113,6 +2115,7 @@ static int mtk_poll_rx(struct napi_struct *napi, int budget,
>  				goto skip_rx;
>  			}
>  
> +			prefetchw(skb->data);

Maybe net_prefetchw instead, as mentioned above?

>  			skb_reserve(skb, xdp.data - xdp.data_hard_start);
>  			skb_put(skb, xdp.data_end - xdp.data);
>  			skb_mark_for_recycle(skb);
> @@ -2143,6 +2146,7 @@ static int mtk_poll_rx(struct napi_struct *napi, int budget,
>  			dma_unmap_single(eth->dma_dev, ((u64)trxd.rxd1 | addr64),
>  					 ring->buf_size, DMA_FROM_DEVICE);
>  
> +			net_prefetch(data);
>  			skb = build_skb(data, ring->frag_size);
>  			if (unlikely(!skb)) {
>  				netdev->stats.rx_dropped++;
> @@ -2150,6 +2154,7 @@ static int mtk_poll_rx(struct napi_struct *napi, int budget,
>  				goto skip_rx;
>  			}
>  
> +			prefetchw(skb->data);

Maybe net_prefetchw instead, as mentioned above?