linux-kernel - Re: [PATCH V5 4/6 net-next] vhost: vhost TX zero-copy support

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Message-ID: <1305646444.10756.16.camel@localhost.localdomain>
Date:	Tue, 17 May 2011 08:34:04 -0700
From:	Shirley Ma <mashirle@...ibm.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	David Miller <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Avi Kivity <avi@...hat.com>, Arnd Bergmann <arnd@...db.de>,
	netdev@...r.kernel.org, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V5 4/6 net-next] vhost: vhost TX zero-copy support

On Tue, 2011-05-17 at 18:28 +0300, Michael S. Tsirkin wrote:
> Which is the order the descriptors are put on avail ring.
> By design, guest should not depend on used ring entries
> being in order with avail ring (and btw with virtio block,
> they aren't). If it does, it's a bug I think.

Ok, I thought, the order should be maintained.

> > The original code has no problem, because it gets one head and pass
> that
> > head to vhost_add_used one by one once done the copy. So it's in
> > sequence.
> > 
> > This issue can easily recreate without zerocopy patch by simply
> changing
> > the order from "head return vhost_get_vq_desc" when passing to
> > vhost_add_used.
> > 
> > Thanks
> > Shirley
> 
> Ah, did you try that? Could you post this patch pls?
> This seems to imply a bug in guest virtio. 

I am creating the patch against net-next for you to test today.

Thanks
Shirley

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