netdev - RE: [PATCH] ethtool: add one ethtool option to set relax ordering mode

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Date:   Fri, 23 Dec 2016 00:40:23 +0000
From:   maowenan <maowenan@...wei.com>
To:     Alexander Duyck <alexander.duyck@...il.com>
CC:     Stephen Hemminger <stephen@...workplumber.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "jeffrey.t.kirsher@...el.com" <jeffrey.t.kirsher@...el.com>,
        "weiyongjun (A)" <weiyongjun1@...wei.com>,
        Dingtianhong <dingtianhong@...wei.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: 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.
-Wenan