netdev - Re: [PATCH] xen/netfront: handle compound page fragments on transmit

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Message-ID: <1353423941.13542.47.camel@zakaz.uk.xensource.com>
Date:	Tue, 20 Nov 2012 15:05:41 +0000
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Konrad Rzeszutek Wilk <konrad@...nel.org>,
	ANNIE LI <annie.li@...cle.com>,
	Sander Eikelenboom <linux@...elenboom.it>,
	"Stefan Bader" <stefan.bader@...onical.com>
Subject: Re: [PATCH] xen/netfront: handle compound page fragments on transmit

On Tue, 2012-11-20 at 14:45 +0000, Eric Dumazet wrote:
> > +		/* Skip unused frames from start of page */
> 
> 'frame' in the comment means an order-0 page ?

Yes. Confusing in the context of a network driver I know! I couldn't
think of a better term.

> > +			id = get_id_from_freelist(&np->tx_skb_freelist, np->tx_skbs);
> > +			np->tx_skbs[id].skb = skb_get(skb);
> 
> BTW this skb_get() means extra atomic operations for every 4096 bytes
> unit, and an extra atomic op (and test for final 0) at TX completion.
> This could be avoided, by setting np->tx_skbs[id].skb = skb only for the
> very last unit.

Thanks. Might be tricky because guests can ack the individual requests
in any order but it's something worth having a look at.

> >  	np->tx.req_prod_pvt = prod;
> 
> Acked-by: Eric Dumazet <edumazet@...gle.com>
> 
> Thanks !

Thanks for the review.

Ian.

> 
> 


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