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SubjectRe: [PATCH] remove fullflush and nofullflush in IOMMU generic option

* FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> wrote:

> This patch against tip/x86/iommu virtually reverts
> 2842e5bf3115193f05dc9dac20f940e7abf44c1a. But just reverting the
> commit breaks AMD IOMMU so this patch also includes some fixes.
>
> The above commit adds new two options to x86 IOMMU generic kernel boot
> options, fullflush and nofullflush. But such change that affects all
> the IOMMUs needs more discussion (all IOMMU parties need the chance to
> discuss it):
>
> http://lkml.org/lkml/2008/9/19/106
>
> For me, adding these boot parameters doesn't make sense.
>
> All the hardware IOMMUs could use 'fullflush' for lazy IOTLB flushing
> but Calgary doesn't support it. Intel VT-d has the different option
> for it (and we can't rename it). [...]

Well if the new option is desired, you dont have to rename the old
option - just alias it to the new too and deprecate the old one
eventually. Boot options are not really ABIs in the traditional sense
anyway.

But, in general, it's pretty pointless to add boot options for anything
but debugging - nobody will use them unless there's a _problem_ with the
default. So the right approach is to not add boot options and to make
sure that the defaults are sane and intelligent.

So could we work towards removing unnecessary boot options please? _If_
we want any strategy switch then that should be runtime anyway - nobody
sane will reboot a server just to tune it slightly, and no distro will
litter the boot commandline with hardware dependent tunings either. So
it's only the default that matters, plus boot parameters for debugging.

Ingo


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