Re: [Xen-devel] [PATCH v2] AMD/intremap: Prevent use of per-device vector maps until irq logic is fixed

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 06/03/2013 03:07 PM, Jan Beulich wrote:
> > > > On 31.05.13 at 22:04, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> > In an effort to get AMD systems back to a non-regressed state, introduce a
> > new
> > type of vector map called per-device-global.  This uses per-device vector maps
> > in the IOMMU, but uses a single used_vector map for the core IRQ logic.
> So what's the reason for not simply using OPT_IRQ_VECTOR_MAP_GLOBAL
> here?
>
> > This patch is intended to be removed as soon as the per-device logic is fixed
> > correctly.
> As a last resort thing this may be acceptable, but I'd much favor to
> fix this properly rather than hacking it like this. Hence I'd really like
> to put up for discussion to instead use the patch[1] already posted
> as preparatory for the multi-vector MSI support doing away with the
> use of the vector for indexing the IRTE (and, in a second patch[2],
> the enforcement of OPT_IRQ_VECTOR_MAP_PERDEV).
Unfortunately this is the time of the release to do simple hacks.  We 
can obviously back this out when we get hte multi-vector MSI suport in.

> Also, overriding a command line request in the way you do is a
> no-go imo - even if this would cause [theoretical] problems, we
> ought to honor the request as long as we can't tell for sure that
> this is going to break the specific system. That's even more so
> since requesting per-device vector maps to be used on VT-d ought
> to yield exactly the same effect, yet you don't override the mode
> there.
I agree -- we need to have a sensible default, but we also need to have 
a way to override behavior if it turns out to cause a problem.
 -George

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