netdev - Re: [Xen-devel] [PATCH net-next V3 2/3] xen-netfront: split event channels support for Xen frontend driver

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Message-ID: <20130523134618.GA18648@zion.uk.xensource.com>
Date:	Thu, 23 May 2013 14:46:18 +0100
From:	Wei Liu <wei.liu2@...rix.com>
To:	Wei Liu <liuw@...w.name>
CC:	annie li <annie.li@...cle.com>, Wei Liu <wei.liu2@...rix.com>,
	Ian Campbell <ian.campbell@...rix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	David Vrabel <david.vrabel@...rix.com>,
	jbeulich <jbeulich@...e.com>
Subject: Re: [Xen-devel] [PATCH net-next V3 2/3] xen-netfront: split event
 channels support for Xen frontend driver

On Wed, May 22, 2013 at 09:38:20PM +0100, Wei Liu wrote:
> On Wed, May 22, 2013 at 9:35 PM, annie li <annie.li@...cle.com> wrote:
> >
> > On 2013-5-22 16:20, Wei Liu wrote:
> >>
> >> On Wed, May 22, 2013 at 8:32 PM, annie li <annie.li@...cle.com> wrote:
> >>>
> >>>
> >>> Originally, netfront protects access to rx shared-ring with tx_lock, you
> >>> remove this protection here. It is better to protect the ring access by a
> >>> sperate rx_lock then.
> >>>
> >> TX ring and RX ring are separate rings. I don't think that comment / code
> >> makes sense any more. My stress test confirms that.
> >
> >
> > Yes, they are separate rings. Actually I am not sure why
> > RING_HAS_UNCONSUMED_RESPONSES(&np->rx) is protected by any tx_lock
> > originally. But for xennet_rx_interrupt, it is better to use rx_lock to
> > protect RING_HAS_UNCONSUMED_RESPONSES(&np->rx).
> >
> 
> This doesn't make sense to me either. Xen ring protocol is designed to
> be lock-free.
> And in netfront's case there is no concurrent access to the ring.
> 
> 

Annie, did I answer your questions / relieve your concern?


Wei.
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