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

From: annie li <[email-masked]>
Date: Thu, 28 Feb 2013 20:55:02 +0800

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