netdev - Re: [PATCH 6/8] netfront: multi-page ring support

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Message-ID: <512F53A6.4000401@oracle.com>
Date:	Thu, 28 Feb 2013 20:55:02 +0800
From:	annie li <annie.li@...cle.com>
To:	Wei Liu <wei.liu2@...rix.com>
CC:	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>
Subject: Re: [PATCH 6/8] netfront: multi-page ring support


On 2013-2-28 19:02, Wei Liu wrote:
> On Thu, Feb 28, 2013 at 05:19:43AM +0000, ANNIE LI wrote:
>> I checked the code in Konrad's tree and am thinking this overlap issue
>> you mentioned existing in original netback(without multi-ring) and newer
>> netfront. Original netback does not support multi-ring, and your newer
>> netfront before this bug fix used "#define TX_MAX_TARGET
>> XENNET_MAX_TX_RING_SIZE" directly. So that would cause overlap when
>> netfront allocating rx skbs.
>> "#define TX_MAX_TARGET min_t(int, NET_TX_RING_SIZE(1), 256)" limits the
>> netfront to single ring, it fixed the overlap issue, but not enough.
>>
> Yes. I just saw a bug report from Xen-user list yesterday for the same
> issue in original netback (1 page ring), so the overlap issue is not
> introduced by multi-page ring implementation. If your team also sees that
> issue, do you have patch to fix that?

No. We thought your patch fixed it, and I did not check it further at 
that time.
Are you sure they are same? What is the thread title in Xen-user?
The overlap issue here exists in netfront when netfront allocates skb 
greedily. In Konrad's tree merged with your patch, netfront with 
"#define TX_MAX_TARGET XENNET_MAX_TX_RING_SIZE" should hit this overlap 
issue when it runs with single ring netback.

Thanks
Annie
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