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

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Date:	Wed, 17 Jul 2013 17:45:51 +0000
From:	Haiyang Zhang <haiyangz@...rosoft.com>
To:	Joseph Salisbury <joseph.salisbury@...onical.com>,
	Pravin Shelar <pshelar@...ira.com>
CC:	"davem@...emloft.net" <davem@...emloft.net>,
	"ben.howard@...onical.com" <ben.howard@...onical.com>,
	"edumazet@...gle.com" <edumazet@...gle.com>,
	"xiyou.wangcong@...il.com" <xiyou.wangcong@...il.com>,
	"alexander.h.duyck@...el.com" <alexander.h.duyck@...el.com>,
	"jiri@...nulli.us" <jiri@...nulli.us>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	KY Srinivasan <kys@...rosoft.com>
Subject: RE: [Regression][v3.10][v3.11] net: Kill link between CSUM and SG
 features.



> -----Original Message-----
> From: Joseph Salisbury [mailto:joseph.salisbury@...onical.com]
> Sent: Wednesday, July 17, 2013 8:31 AM
> To: Pravin Shelar
> 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; KY Srinivasan; Haiyang Zhang
> 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.
I have submitted a patch which has been accepted, and queued for -stable branch
as well: http://patchwork.ozlabs.org/patch/259596/
It removes the NETIF_F_SG flag from the hv_netvsc driver, which doesn't currently
support SG mode.

Thanks,
- Haiyang

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