linux-kernel - Re: [PATCH net-next v1 3/3] net: stmmac: Optimize cache prefetch in RX path

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Message-ID: <20250113203710.000033dc@gmail.com>
Date: Mon, 13 Jan 2025 20:37:10 +0800
From: Furong Xu <0x1207@...il.com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>
Cc: <netdev@...r.kernel.org>, <linux-stm32@...md-mailman.stormreply.com>,
 <linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
 Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
 <kuba@...nel.org>, "Paolo Abeni" <pabeni@...hat.com>, Maxime Coquelin
 <mcoquelin.stm32@...il.com>, <xfr@...look.com>
Subject: Re: [PATCH net-next v1 3/3] net: stmmac: Optimize cache prefetch in
 RX path

On Mon, 13 Jan 2025 13:10:46 +0100, Alexander Lobakin <aleksander.lobakin@...el.com> wrote:

> > @@ -5596,6 +5593,7 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
> >  		} else if (buf1_len) {
> >  			dma_sync_single_for_cpu(priv->device, buf->addr,
> >  						buf1_len, dma_dir);
> > +			prefetch(page_address(buf->page) + buf->page_offset);
> >  			skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags,
> >  					buf->page, buf->page_offset, buf1_len,
> >  					priv->dma_conf.dma_buf_sz);  
> 
> Are you sure you need to prefetch frags as well? I'd say this is a waste
> of cycles, as the kernel core stack barely looks at payload...
> Probably prefetching only header buffers would be enough.
> 

Yes, do not prefetch for frags is more reasonable.
Thanks!

pw-bot: changes-requested