netdev - Re: [PATCH 2/6] net: mvneta: move skb build after descriptors processing

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Message-ID: <20200716200909.GJ2174@localhost.localdomain>
Date:   Thu, 16 Jul 2020 22:09:09 +0200
From:   Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Lorenzo Bianconi <lorenzo@...nel.org>, netdev@...r.kernel.org,
        davem@...emloft.net, bpf@...r.kernel.org,
        ilias.apalodimas@...aro.org, brouer@...hat.com,
        echaudro@...hat.com, sameehj@...zon.com
Subject: Re: [PATCH 2/6] net: mvneta: move skb build after descriptors
 processing

> On Thu, 16 Jul 2020 21:12:51 +0200 Lorenzo Bianconi wrote:
> > > > +static struct sk_buff *
> > > > +mvneta_swbm_build_skb(struct mvneta_port *pp, struct mvneta_rx_queue *rxq,
> > > > +		      struct xdp_buff *xdp, u32 desc_status)
> > > > +{
> > > > +	struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp);
> > > > +	int i, num_frags = sinfo->nr_frags;
> > > > +	skb_frag_t frags[MAX_SKB_FRAGS];
> > > > +	struct sk_buff *skb;
> > > > +
> > > > +	memcpy(frags, sinfo->frags, sizeof(skb_frag_t) * num_frags);
> > > > +
> > > > +	skb = build_skb(xdp->data_hard_start, PAGE_SIZE);
> > > > +	if (!skb)
> > > > +		return ERR_PTR(-ENOMEM);
> > > > +
> > > > +	page_pool_release_page(rxq->page_pool, virt_to_page(xdp->data));
> > > > +
> > > > +	skb_reserve(skb, xdp->data - xdp->data_hard_start);
> > > > +	skb_put(skb, xdp->data_end - xdp->data);
> > > > +	mvneta_rx_csum(pp, desc_status, skb);
> > > > +
> > > > +	for (i = 0; i < num_frags; i++) {
> > > > +		skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags,
> > > > +				frags[i].bv_page, frags[i].bv_offset,
> > > > +				skb_frag_size(&frags[i]), PAGE_SIZE);
> > > > +		page_pool_release_page(rxq->page_pool, frags[i].bv_page);
> > > > +	}
> > > > +
> > > > +	return skb;
> > > > +}  
> > > 
> > > Here as well - is the plan to turn more of this function into common
> > > code later on? Looks like most of this is not really driver specific.  
> > 
> > I agree. What about adding it when other drivers will add multi-buff support?
> > (here we have even page_pool dependency)
> 
> I guess that's okay on the condition that you're going to be the one
> adding the support to the next driver, or at least review it very
> closely to make sure it's done.

I am completely fine to work on it if I have the hw handy (or if someone else
can test it) otherwise I will review the code :)

Regards,
Lorenzo

> 
> In general vendors prove rather resistant to factoring code out, 
> the snowflakes they feel they are.
> 

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