netdev - Re: [Regression][v3.10][v3.11] net: Kill link between CSUM and SG features.

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Date:	Wed, 17 Jul 2013 11:30:56 -0400
From:	Joseph Salisbury <joseph.salisbury@...onical.com>
To:	Pravin Shelar <pshelar@...ira.com>
CC:	davem@...emloft.net, ben.howard@...onical.com, edumazet@...gle.com,
	xiyou.wangcong@...il.com, alexander.h.duyck@...el.com,
	jiri@...nulli.us, netdev@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>, kys@...rosoft.com,
	haiyangz@...rosoft.com
Subject: Re: [Regression][v3.10][v3.11] net: Kill link between CSUM and SG
 features.

On 07/16/2013 04:50 PM, Pravin Shelar wrote:
> On Tue, Jul 16, 2013 at 12:53 PM, Joseph Salisbury
> <joseph.salisbury@...onical.com> wrote:
>> On 07/16/2013 02:29 PM, Pravin Shelar wrote:
>>> On Tue, Jul 16, 2013 at 11:09 AM, Joseph Salisbury
>>> <joseph.salisbury@...onical.com> wrote:
>>>> Hi Pravin,
>>>>
>>>> A bug was opened against the Ubuntu kernel[0].  After a kernel bisect,
>>>> it was found that reverting the following commit resolved this bug:
>>>>
>>>> commit ec5f061564238892005257c83565a0b58ec79295
>>>> Author: Pravin B Shelar <pshelar@...ira.com>
>>>> Date:   Thu Mar 7 09:28:01 2013 +0000
>>>>
>>>>     net: Kill link between CSUM and SG features.
>>>>
>>>>
>>>> The regression was introduced as of v3.10-rc1.
>>>>
>>>> I see that you are the author of this patch, so I wanted to run this by
>>>> you.  I was thinking of requesting a revert for v3.11, but I wanted to
>>>> get your feedback first.
>>>>
>>>>
>>> This issue was reported before and turning off sg solves problem for
>>> HyperV driver. Drivers (intel and bnx2x) that I tested works fine with
>>> this patch. Have you seen the issue on any other NIC?
>> Thanks for the feedback.  We have only seen it on Intel hardware.  Can
>> you send a pointer to the patch? If so, we can provide some additional
>> testing.  Do you plan on submitting the patch for inclusion in 3.11?
>>
>>
> What I mean is I do not see any problem with the patch that you have
> pointed out on ixgbe and bnx2x platforms. HyperV problem went away
> with disabling sg by ethtool utility.
Yes, we also see that the problem goes away when disabling sg with
ethtool.  There was a significant improvement in throughput with sg
enabled, so it's unfortunate it must be disabled. 

>
> Can you also give me more information about regression you are seeing
> like driver name, features of the NIC set and features of device
> without this patch. Does any other NIC than HyperV having this issue?

Some details info about the HyperV guest can be seen here:
http://paste.ubuntu.com/5884549/

In that output, you will see that scatter-gather is off, which was done
manually. 

Only a HyperV NIC is having this issue.

>
> Thanks.
>
>>>
>>>> Thanks,
>>>>
>>>> Joe
>>>>
>>>> [0] http://pad.lv/1200243
>>>>
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