Re: [Xen-devel] heavy P2M lock contention on guest HPET counter reads

[Andres Lagar Cavilla <andres@xxxxxxxxxxxxxxxx>]

On Fri, Aug 1, 2014 at 2:38 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote:

>>> On 30.07.14 at 20:15, <andres@xxxxxxxxxxxxxxxx> wrote:
> Having said that, I don't know off the top of my head that is obviously
> correct to shortcut the p2m lookup for msix table and iommu. I think so,
> but...

All internal MMIO ranges are what you'd call "positively decoded" on
real hardware, i.e. they ought to supersede any other address
decoding rules anyway. Since they're also not associated with
possibly varying MFNs, the P2M lookup on them is simply pointless,
and short-circuiting them is imo at once making better guarantees
towards consistent behavior.

Ok. Good. However: this is a very hot path. I wonder if this iteration can be made more efficient (i.e sort the resulting mmio regions and do binary search).

AndresÂ

Jan

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