Re: DPDK packaging and OpenWrt

[Garrett D'Amore <garrett@damore.org>]

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On May 16, 2023 at 12:19 PM -0700, Philip Prindeville <philipp_subx@redfish-solutions.com>, wrote:
> Hi,
>
> I'm a packaging maintainer for some of the OpenWrt ancillary packages, and I'm looking at upstreaming DPDK support into OpenWrt. Apologies in advance if this is a bit dense (a brain dump) or hops between too many topics.
>
> I was looking at what's been done to date, and it seems there are a few shortcomings which I hope to address.
>
> Amongst them are:
>
>
> I have some related questions.
>
> 1. OpenWrt already bakes "vfio.ko" and "vfio-pci.ko" here:
>
> https://github.com/openwrt/openwrt/blob/master/package/kernel/linux/modules/virt.mk#L77-L117
>
> but does so with "CONFIG_VFIO_PCI_IGD=y", which seems to be specifically for VGA acceleration of guests in a virtualized environment. That seems to be an odd corner case, and unlikely given that OpenWrt almost always runs on headless hardware. Should this be reverted?
>
> 2. "vfio.ko" is built with "CONFIG_VFIO_NOIOMMU=y", which seems insecure. Can this be reverted?
>
> 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.
>
> 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


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