Re: DPDK packaging and OpenWrt

[Philip Prindeville <philipp_subx@redfish-solutions.com>]

> On May 16, 2023, at 5:06 PM, Garrett D'Amore <garrett@damore.org> wrote:
> 
> On May 16, 2023 at 12:19 PM -0700, Philip Prindeville <philipp_subx@redfish-solutions.com>, wrote:
> [snip]
> 
> 3. Is "uio_pci_generic.ko" worth the potential insecurity/instability of a misbehaving application? My understanding is that it's only needed on SR-IOV hardware where MSI/MSI-X interrupts aren't supported: is there even any current hardware that doesn't support MSI/MSI-X? Or am I misunderstanding the use case? 
> *Either* uio_pci_generic *or* vfio with NOIOMMU are required for the vary large number of systems that either lack an IOMMU (btw, that will be nearly all OpenWRT platforms!), or elect to run with the iommu unconfigured (one justification for doing that - apart from numerous software bugs and limitations — is that the IOMMU can slow down I/O. We actually recommend most of our customers that run dedicated systems run with the IOMMU disabled for this reason.)
> 
> vfio with  noiommu is preferable.


I could build with CONFIG_NOIOMMU=n and then package the modprobe .conf file (or the grub command-line, etc) to have enable_unsafe_noiommu_mode=1, right?

This would accomplish the same thing at run-time, but allow the module to be built to be used either with or without an IOMMU?

That's per:

https://dpdk-guide.gitlab.io/dpdk-guide/setup/binding.html

But I don't know how recent that advice is...


> 
> 4. Can most functionality be achieved with VFIO + IOMMU support? 
> *If* you have an IOMMU, and you aren’t trying to eke the very last bits of performance, yes.  But as many systems don’t have an IOMMU, and as one of the main points of DPDK are extremely performance sensitive applications, I think the answer is more broadly, “no”.
> 11. What is the user-space TCP/IP stack of choice (or reference) for use with DPDK? 
> IMO, if you’re using DPDK to run *TCP* applications then you’re probably misusing it — there isn’t a user land TCP stack that I would trust.  IP/UDP is something we do, and it works well, but I can tell you already it’s a pain to do *just* IP, because e.g. routing tables, ARP, etc. all have to be handled. 
>     • Garrett


Yeah, good point.  Are there shims to use with FRR, lldpd, et al for example?