hi, all
On 4/15/2018 4:10 AM, Matan Azrad wrote:
Hi all
From: Burakov, Anatoly, Friday, April 13, 2018 8:41 PM
To: Bruce Richardson <bruce.richard...@intel.com>; Thomas Monjalon
<tho...@monjalon.net>
Cc: dev@dpdk.org; pmati...@redhat.com; david.march...@6wind.com;
jia....@intel.com; Matan Azrad <ma...@mellanox.com>;
konstantin.anan...@intel.com; step...@networkplumber.org;
f...@redhat.com
Subject: Re: kernel binding of devices + hotplug
On 13-Apr-18 5:40 PM, Bruce Richardson wrote:
On Fri, Apr 13, 2018 at 06:31:21PM +0200, Thomas Monjalon wrote:
It's time to think (again) how we bind devices with kernel modules.
We need to decide how we want to manage hotplugged devices with
DPDK.
A bit of history first.
There was some code in DPDK for bind/unbind, but it has been removed
in DPDK 1.7 -
https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fdpd
k.org%2Fcommit%2F5d8751b83&data=02%7C01%7Cmatan%40mellanox.com
%7C6ea5
5ce994ff4bb0d65208d5a165b417%7Ca652971c7d2e4d9ba6a4d149256f461b%7
C0%7
C0%7C636592380565078675&sdata=uLRDAk65hYtJYxjIvY20de377yayCN5DrjCZ
x8H
p61o%3D&reserved=0 Copy of the commit message (in 2014):
"
The bind/unbind operations should not be handled by the eal.
These operations should be either done outside of dpdk or
inside the PMDs themselves as these are their problems.
"
The question raised at this time (4 years ago) is still under discussion.
Should we manage binding inside or outside DPDK?
Should it be controlled in the application or in the OS base?
As you know, we use dpdk-devbind.py.
This tool lacks two major features:
- persistent configuration
- hotplug
If we consider that the DPDK applications should be able to apply its
own policy to choose the devices to bind, then we need to implement
binding in the PMD (with EAL helpers).
On the other hand, if we consider that it is the system
responsibility, then we could choose systemd/udev and driverctl.
The debate is launched!
Allow me to nail my colours to the mast early! :-)
I believe it's system not application responsibility.
I also believe I have previously explained my reasons for that choice
in some of the previous email threads.
For what it's worth, I tend to agree, if only because writing code for what is
essentially a bunch of read/write/filesystem enumeration in C is extremely
fiddly and error prone :) IMO things like this are better handled either by
scripts, or by tools whose sole purpose is doing exactly that (or both).
I like having scripts like devbind in DPDK because we can tailor them to our
use cases better, and having them is amenable to automation, but while I
wouldn't be opposed to removing them altogether in favor of some external
tool (systemd/udev/driverctl/whatever), in my humble opinion moving them
back into EAL or even PMD's would be a mistake.
Since the application runs in the system by a command of the system user I
think the responsibility is for the user.
The DPDK user forwards the control of some devices to the DPDK application
using the EAL whitelist\blacklist mode to specify the devices,
Any DPDK PMD should know which binding it needs to probe\control the device and
can apply it,
So, if the user asks to control on a device by DPDK application it makes sense
that the application will do the correct binding to the device since the user
wants to use it(no need to ask more operation of pre binding from the user).
Regarding the conflict of system rules for a device, it is again the user
responsibility, whatever we will decide for the binding procedure of DPDK
application the user needs to take it into account and to solve such like
conflicts.
One option is to remove any binding rules of a DPDK device in the DPDK
application initialization and adjust the new rules by the PMDs, then any
conflict should not disturb the user.
In current hot-plug case the application will need to do a lot of work to
bind\remap devices in plug-in\plug-out events while the PMD could have all the
knowledge to do it.
One more issue with the script is that the user should do different bind per
device, in case of PMD responsibility the user can forget it:
Think about that, any time the user wants to switch\add new supported nic it
should update the script usage and to do per nic operation contrary to the DPDK
principles.
Matan.
Thanks,
Anatoly
when device appear whenever dpdk is runnning or not, the device will
default bind to Kernel driver, user or say system admin could use the
script or tools to rebind a specific driver which according their request
so i think user space tools provide functional and user have the binding
responsibility rather than the app or PMD. i don't understand why over
ride to other driver is the scope of an specific PMD. And if there is
conflict by rules , user could over ride it and take the control.
Per dpdk hotplug, the purpose is for the app failsafe and VM live
migration, driverctl is focus driver control and udev is focus on
device hotplug but no userspace failure handle , there are still not an
complete hotplug solution for dpdk app, even the script have binding,
it look like as a minimal "system admin tools" fit for dpdk, but not
persistent and not hotplug functional. so if we aim to provider a total
hotplug service at dpdk framework, offload these works from application
and user that is need. In normal user take the driver control by
tools/script(both ok in my opinion) optional at initial , while in
hotplug case, failure occur on runtime, dpdk take the control of driver
from user. compare with app and PMD, do you agree dpdk best to take the
role on runtime? if only user could take the role, the SRIOV live
migration of dpdk would hard to be make sense.
i agree let app don't care about any bind/failure handle, in current
hotplug solution failure handle embedded in dpdk but binding is exposed
to app, if got agreement to dpdk binding , i could let dpdk self do it.
if vote result is not let dpdk charge it, i will temporary remove the
binding function to shrink the hotplug scope. postpone it to further
failsafe and live migrate topic.
basically speaking, for binding, script vs tools vs PMD vs dpdk, i vote
dpdk , at lest run time case.
