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: <519E2461.2090203@oracle.com>
Date:	Thu, 23 May 2013 10:14:57 -0400
From:	annie li <annie.li@...cle.com>
To:	Wei Liu <wei.liu2@...rix.com>
CC:	Wei Liu <liuw@...w.name>, 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 2013-5-23 9:46, Wei Liu wrote:
> 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?

Yes, I think you are correct.

Thanks
Annie
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