netdev - Re: [PATCH V6 0/4 net-next] macvtap/vhost TX zero-copy support

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Date:	Sat, 28 May 2011 11:07:03 -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 V6 0/4 net-next] macvtap/vhost TX zero-copy support

On Thu, 2011-05-26 at 13:31 -0700, Shirley Ma wrote:
> On Thu, 2011-05-26 at 23:28 +0300, Michael S. Tsirkin wrote:
> > On Thu, May 26, 2011 at 01:00:20PM -0700, Shirley Ma wrote:
> > > 3. Add sleep in vhost shutting down instead of busy-wait for
> > outstanding
> > >    DMAs.
> > 
> > I still think this is not much better. We need to use a
> > completion structure and wait on it instead.
> > If this gets blocked thinkably a tx watchdog can fire and save us
> > from blocking forver :) 
> 
> Ok, I can add a completion structure here. 

The code here doesn't block forever during shutdown, it will release all
outstanding userspace buffers anyway, see vhost_zerocopy_signal_used()
shutdown case.

Thanks
Shirley

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