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Date:   Sat, 24 Dec 2016 08:30:05 +0000
From:   maowenan <maowenan@...wei.com>
To:     Alexander Duyck <alexander.duyck@...il.com>
CC:     Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "weiyongjun (A)" <weiyongjun1@...wei.com>,
        Dingtianhong <dingtianhong@...wei.com>,
        "Wangzhou (B)" <wangzhou1@...ilicon.com>
Subject: RE: [PATCH] ethtool: add one ethtool option to set relax ordering
 mode



> -----Original Message-----
> From: Alexander Duyck [mailto:alexander.duyck@...il.com]
> Sent: Friday, December 23, 2016 11:43 PM
> To: maowenan
> Cc: Jeff Kirsher; Stephen Hemminger; netdev@...r.kernel.org; weiyongjun (A);
> Dingtianhong
> Subject: Re: [PATCH] ethtool: add one ethtool option to set relax ordering mode
> 
> On Thu, Dec 22, 2016 at 10:14 PM, maowenan <maowenan@...wei.com>
> wrote:
> >
> >
> >> -----Original Message-----
> >> From: Jeff Kirsher [mailto:jeffrey.t.kirsher@...el.com]
> >> Sent: Friday, December 23, 2016 9:07 AM
> >> To: maowenan; Alexander Duyck
> >> Cc: Stephen Hemminger; netdev@...r.kernel.org; weiyongjun (A);
> >> Dingtianhong
> >> Subject: Re: [PATCH] ethtool: add one ethtool option to set relax
> >> ordering mode
> >>
> >> On Fri, 2016-12-23 at 00:40 +0000, maowenan wrote:
> >> > > -----Original Message-----
> >> > > From: Alexander Duyck [mailto:alexander.duyck@...il.com]
> >> > > Sent: Thursday, December 22, 2016 11:54 PM
> >> > > To: maowenan
> >> > > Cc: Stephen Hemminger; netdev@...r.kernel.org;
> jeffrey.t.kirsher@...el.
> >> > > com;
> >> > > weiyongjun (A); Dingtianhong
> >> > > Subject: Re: [PATCH] ethtool: add one ethtool option to set relax
> >> > > ordering mode
> >> > >
> >> > > On Wed, Dec 21, 2016 at 5:39 PM, maowenan
> <maowenan@...wei.com>
> >> > > wrote:
> >> > > >
> >> > > >
> >> > > > > -----Original Message-----
> >> > > > > From: Stephen Hemminger [mailto:stephen@...workplumber.org]
> >> > > > > Sent: Thursday, December 22, 2016 9:28 AM
> >> > > > > To: maowenan
> >> > > > > Cc: netdev@...r.kernel.org; jeffrey.t.kirsher@...el.com
> >> > > > > Subject: Re: [PATCH] ethtool: add one ethtool option to set
> >> > > > > relax ordering mode
> >> > > > >
> >> > > > > On Thu, 8 Dec 2016 14:51:38 +0800 Mao Wenan
> >> > > > > <maowenan@...wei.com> wrote:
> >> > > > >
> >> > > > > > This patch provides one way to set/unset IXGBE NIC TX and
> >> > > > > > RX relax ordering mode, which can be set by ethtool.
> >> > > > > > Relax ordering is one mode of 82599 NIC, to enable this
> >> > > > > > mode can enhance the performance for some cpu architecure.
> >> > > > >
> >> > > > > Then it should be done by CPU architecture specific quirks
> >> > > > > (preferably in PCI
> >> > > > > layer) so that all users get the option without having to do
> >> > > > > manual
> >> > >
> >> > > intervention.
> >> > > > >
> >> > > > > > example:
> >> > > > > > ethtool -s enp1s0f0 relaxorder off ethtool -s enp1s0f0
> >> > > > > > relaxorder on
> >> > > > >
> >> > > > > Doing it via ethtool is a developer API (for testing) not
> >> > > > > something that makes sense in production.
> >> > > >
> >> > > >
> >> > > > This feature is not mandatory for all users, acturally relax
> >> > > > ordering default configuration of 82599 is 'disable', So this
> >> > > > patch gives one way to
> >> > >
> >> > > enable relax ordering to be selected in some performance condition.
> >> > >
> >> > > That isn't quite true.  The default for Sparc systems is to have
> >> > > it enabled.
> >> > >
> >> > > Really this is something that is platform specific.  I agree with
> >> > > Stephen that it would work better if this was handled as a series
> >> > > of platform specific quirks handled at something like the PCI
> >> > > layer rather than be a switch the user can toggle on and off.
> >> > >
> >> > > With that being said there are changes being made that should
> >> > > help to improve the situation.  Specifically I am looking at
> >> > > adding support for the DMA_ATTR_WEAK_ORDERING which may also
> >> > > allow us to identify cases where you might be able to specify the
> >> > > DMA behavior via the DMA mapping instead of having to make the
> >> > > final decision in the device itself.
> >> > >
> >> > > - Alex
> >> >
> >> > Yes, Sparc is a special case. From the NIC driver point of view, It
> >> > is no need for some ARCHs to do particular operation and compiling
> >> > branch, ethtool is a flexible method for user to make decision
> >> > whether
> >> > on|off this feature.
> >> > I think Jeff as maintainer of 82599 has some comments about this.
> >>
> >> My original comment/objection was that you attempted to do this
> >> change as a module parameter to the ixgbe driver, where I directed
> >> you to use ethtool so that other drivers could benefit from the
> >> ability to enable/disable relaxed ordering.  As far as how it gets
> >> implemented in ethtool or PCI layer, makes little difference to me, I
> >> only had issues with the driver specific module parameter implementation,
> which is not acceptable.
> >
> >
> > Thank you Jeff and Alex.
> > And then I have gone through mail thread about "i40e: enable PCIe
> > relax ordering for SPARC", It only works for SPARC, any other ARCH who
> > wants to enable DMA_ATTR_WEAK_ORDERING feature, should define the
> new macro, recompile the driver module.
> >
> > Because of the above reasons, we implement in ethtool to give the
> > final user a convenient way to on|off special feature, no need define
> > new macro, easy to extend the new features, and also good benefit for other
> driver as Jeff referred.
> >
> 
> I think the point is we shouldn't base the decision on user input.
> The fact is the PCIe device control register should have a bit that indicates if
> the device is allowed to enable relaxed ordering or not.
> If we can guarantee that the bit is set in all the cases where it should be set,
> and cleared in all the cases where it should not then we could use something
> like that to determine if the device is supposed to enable relaxed ordering
> instead of trying to make the decision ourselves.
> 
> - Alex

ok. We are focusing on the register. 
And yes, to enable relax ordering for 82599 should be set by one or more bits of Rx/TX DCA Control 
Register, these bits should be set in many cpu architectures, such as arm64, sparc, and so on, and 
should be cleared in other ARCHs.
By the way, how do you enable SPARC macro, how and where to define this compiling macro when user 
one to enable relax ordering under SPARC system?  
#ifndef CONFIG_SPARC



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