RE: Clarification on Minimum Supported Kernel Version for DPDK

RE: Clarification on Minimum Supported Kernel Version for DPDK

[Morten Brørup]

@Kevin, @Stephen, @Bruce,

I cannot reliably answer Cody's question, and it may need further discussion.

What is your opinion on minimum Linux kernel version requirements?

@Thomas: In the future, the DPDK release notes should mention the minimum Linux kernel requirements.

> From: Cody Cheng [mailto:ccheng@iol.unh.edu]
> Sent: Thursday, 20 March 2025 21.28
> 
> Hi Morten,
> 
> I am in the process of setting up a test environment at the UNH DPDK
> Community Test Lab that follows the minimum supported kernel version
> for DPDK. According to the DPDK documentation, the minimum supported
> kernel version is 4.19. However, the oldest long term stable kernel
> version listed on kernel.org is 5.4.291.
> 
> Should the test environment be set up on kernel version 4.19 or
> 5.4.291?

The kernel 4.19 support stems from still supporting RHEL/CentOS 7.
I wonder if this exception mentioned in the documentation [1] is still valid, or if we should bump it to RHEL/CentOS 8, which ships with kernel 4.18 [1].

RHEL/CentOS 7 support was discussed at by tech board long ago [2], but I cannot find a conclusion about the kernel version; the discussion was mostly about compiler support.

[1]: https://doc.dpdk.org/guides/linux_gsg/sys_reqs.html#system-software
[2]: https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/8/html-single/8.0_release_notes/index#overview
[3]: https://mails.dpdk.org/archives/dev/2023-February/263516.html


> 
> Thanks,
> Cody Cheng
> UNH DPDK Community Test Lab

Re: Clarification on Minimum Supported Kernel Version for DPDK

[Bruce Richardson]

On Fri, Mar 21, 2025 at 07:28:45AM +0100, Morten Brørup wrote:
> @Kevin, @Stephen, @Bruce,
> 
> I cannot reliably answer Cody's question, and it may need further discussion.
> 
> What is your opinion on minimum Linux kernel version requirements?
> 
> @Thomas: In the future, the DPDK release notes should mention the minimum Linux kernel requirements.
> 

Another question is - should we even have a minimum kernel version? Are we
aware of any kernel features beyond vfio-pci driver which DPDK requires to
run? As a userspace application, I think DPDK should just work with
whatever distro-provided kernel is provided (assuming distro is relatively
recent).

/Bruce

RE: Clarification on Minimum Supported Kernel Version for DPDK

[Morten Brørup]

> From: Bruce Richardson [mailto:bruce.richardson@intel.com]
> 
> On Fri, Mar 21, 2025 at 07:28:45AM +0100, Morten Brørup wrote:
> > @Kevin, @Stephen, @Bruce,
> >
> > I cannot reliably answer Cody's question, and it may need further
> discussion.
> >
> > What is your opinion on minimum Linux kernel version requirements?
> >
> > @Thomas: In the future, the DPDK release notes should mention the
> minimum Linux kernel requirements.
> >
> 
> Another question is - should we even have a minimum kernel version? Are
> we
> aware of any kernel features beyond vfio-pci driver which DPDK requires
> to
> run?
> As a userspace application, I think DPDK should just work with
> whatever distro-provided kernel is provided (assuming distro is
> relatively
> recent).

I agree regarding distros.

However, embedded systems may be stuck on ancient kernel versions for a variety of reasons.
Documenting the explicit requirements to the kernel are relevant for these.

I would expect all of the DPDK's EAL to behave as expected, so this should be the basis for defining DPDK's minimum kernel requirements - regarding both kernel version and optional kernel features required.
<noise>
In this context, "all of the EAL" really should mean the core of the EAL, exclusive the non-optional bloat that has nothing to do with abstracting the HW and O/S, and thus shouldn't be part of the EAL. But for now, I think we need to consider the EAL as-is, incl. any bloat.
</noise>

Some DPDK drivers may have additional kernel requirements.
Any such requirements should be documented with the individual drivers.
And, preferably, any driver should be able to degrade its capabilities gracefully when some optional requirements are not fulfilled.

In other words: We don't want DPDK's minimum kernel requirements to depend on some driver requiring some new and shiny kernel feature - the minimum kernel requirements should only depend on the EAL.

And - going back to the original question, triggering this discussion - we need to settle on a minimum kernel version for the CI testing at UNH.

Re: Clarification on Minimum Supported Kernel Version for DPDK

[Stephen Hemminger]

On Fri, 21 Mar 2025 07:28:45 +0100
Morten Brørup <mb@smartsharesystems.com> wrote:

> @Kevin, @Stephen, @Bruce,
> 
> I cannot reliably answer Cody's question, and it may need further discussion.
> 
> What is your opinion on minimum Linux kernel version requirements?
> 
> @Thomas: In the future, the DPDK release notes should mention the minimum Linux kernel requirements.
> 
> > From: Cody Cheng [mailto:ccheng@iol.unh.edu]
> > Sent: Thursday, 20 March 2025 21.28
> > 
> > Hi Morten,
> > 
> > I am in the process of setting up a test environment at the UNH DPDK
> > Community Test Lab that follows the minimum supported kernel version
> > for DPDK. According to the DPDK documentation, the minimum supported
> > kernel version is 4.19. However, the oldest long term stable kernel
> > version listed on kernel.org is 5.4.291.
> > 
> > Should the test environment be set up on kernel version 4.19 or
> > 5.4.291?  
> 
> The kernel 4.19 support stems from still supporting RHEL/CentOS 7.
> I wonder if this exception mentioned in the documentation [1] is still valid, or if we should bump it to RHEL/CentOS 8, which ships with kernel 4.18 [1].
> 
> RHEL/CentOS 7 support was discussed at by tech board long ago [2], but I cannot find a conclusion about the kernel version; the discussion was mostly about compiler support.
> 
> [1]: https://doc.dpdk.org/guides/linux_gsg/sys_reqs.html#system-software
> [2]: https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/8/html-single/8.0_release_notes/index#overview
> [3]: https://mails.dpdk.org/archives/dev/2023-February/263516.html

My opinion has always been that DPDK only offers certain guarantees about testing:
  - oldest current LTS
  - oldest supported version of Redhat/Ubuntu/SUSE enterprise kernels

after that in the embedded space, the user is likely to be ok but any kernel
related issues are their problem not the communities to deal with.

The two parts most likely to cause issues are vfio-pci and vhost related stuff.
There is also small chance of issues with the memory handling in EAL.