Re: [PATCH] PCI: vmd: Do not disable MSI-X remapping in VMD 28C0 controller

[Keith Busch]

On Tue, Feb 07, 2023 at 01:32:20PM -0700, Patel, Nirmal wrote:
> On 2/6/2023 8:18 PM, Xinghui Li wrote:
> > Keith Busch <kbusch@xxxxxxxxxx> 于2023年2月7日周二 02:28写道：
> >> I suspect bypass is the better choice if "num_active_cpus() > pci_msix_vec_count(vmd->dev)".
> > For this situation, My speculation is that the PCIE nodes are
> > over-mounted and not just because of the CPU to Drive ratio.
> > We considered designing online nodes, because we were concerned that
> > the IO of different chunk sizes would adapt to different MSI-X modes.
> > I privately think that it may be logically complicated if programmatic
> > judgments are made.
> 
> Also newer CPUs have more MSIx (128) which means we can still have
> better performance without bypass. It would be better if user have
> can chose module parameter based on their requirements. Thanks.

So what? More vectors just pushes the threshold to when bypass becomes
relevant, which is exactly why I suggested it. There has to be an empirical
answer to when bypass beats muxing. Why do you want a user tunable if there's a
verifiable and automated better choice?