Re: [PATCH v5] PCI: vmd: Add the module param to adjust MSI mode

Bjorn Helgaas
2023-04-28T19:58:29Z

On Fri, Apr 28, 2023 at 01:40:36PM -0500, Bjorn Helgaas wrote:
> On Thu, Apr 20, 2023 at 03:09:14PM +0800, korantwork@gmail.com wrote:
> > From: Xinghui Li <korantli@tencent.com>

> What if you made boolean parameters like these:
>
> no_msi_remap
>
> If the VMD supports it, disable VMD MSI-X remapping. This
> improves interrupt performance because child device interrupts
> avoid the VMD MSI-X domain interrupt handler.
>
> msi_remap
>
> Remap child MSI-X interrupts into VMD MSI-X interrupts. This
> limits the number of MSI-X vectors available to the whole child
> device domain to the number of VMD MSI-X interrupts.

I guess having two parameters that affect the same feature is also
confusing. Maybe just "msi_remap=0" or "msi_remap=1" or something?

I think what makes "disable_msi_bypass=0" hard is that "MSI bypass" by
itself is a negative feature (the positive activity is MSI remapping),
and disabling bypass gets us back to the positive "MSI remapping"
situation, and "disable_msi_bypass=0" negates that again, so we're
back to ... uh ... let's see ... we are not disabling the bypass of
MSI remapping, so I guess MSI remapping would be *enabled*? Is that
right?

Bjorn