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

-----Original Message-----
From: Alexander Duyck [mailto:alexander.duyck@gmail.com]
Sent: Thursday, December 22, 2016 11:54 PM
To: maowenan
Cc: Stephen Hemminger; netdev@vger.kernel.org; jeffrey.t.kirsher@intel.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 [off-list ref]
wrote:

quoted

quoted

-----Original Message-----
From: Stephen Hemminger [mailto:stephen@networkplumber.org]
Sent: Thursday, December 22, 2016 9:28 AM
To: maowenan
Cc: netdev@vger.kernel.org; jeffrey.t.kirsher@intel.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 [off-list ref] wrote:

quoted

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.

quoted

quoted

quoted

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