netdev - Re: PATCH v2 3/4] Defer skb allocation -- new recvbuf alloc & receive calls

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Message-ID: <20091215163901.GA24015@redhat.com>
Date:	Tue, 15 Dec 2009 18:39:01 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Shirley Ma <mashirle@...ibm.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>, Avi Kivity <avi@...hat.com>,
	netdev@...r.kernel.org, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Anthony Liguori <anthony@...emonkey.ws>
Subject: Re: PATCH v2 3/4] Defer skb allocation -- new recvbuf alloc &
	receive calls

On Tue, Dec 15, 2009 at 08:25:20AM -0800, Shirley Ma wrote:
> On Tue, 2009-12-15 at 13:33 +0200, Michael S. Tsirkin wrote:
> > So what I would suggest is, have function
> > that just copies part of skb, and have
> > caller open-code allocating the skb and free up
> > pages as necessary.
> Yes, the updated patch has changed the function.
> 
> > What I am asking is why do we add skb in vi->recv.
> > Can't we use vq destoy hack here as well?
> Yes, I removed recv queue skb link totally in the updated patch.
> 
> > > One is for big packet virtio_net_hdr, one is for goodcopy skb.
> > 
> > 
> > Maybe put this in a comment then.
> Ok, will do.
> 
> > 
> > I mean the for loop: can i be for(i = 0, ..., ++i) just as well?
> > Why do you start at the end of buffer and decrement?
> 
> Are asking why reverse order for new page to sg? The reason is we link
> the new page in first, and only maintain the first pointer. So the most
> recent new page should be related to sg[0], if we put the new page in
> the last, then we need to travel the page list to get last pointer. Am I
> missing your point here?
> 
> Thanks
> Shirley 


No, that was what I was looking for.

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