On Wed, Jun 10, 2020 at 11:37:14PM +0200, Halil Pasic wrote: > On Wed, 10 Jun 2020 14:25:54 +1000 > David Gibson <da...@gibson.dropbear.id.au> wrote: > > > > > I'm going to definitely have a good look at that. What I think special > > > > about s390 is that F_ACCESS_PLATFORM is hurting us because all IO needs > > > > to go through ZONE_DMA (this is a problem of the implementation that > > > > stemming form a limitation of the DMA API, upstream didn't let me > > > > fix it). > > > > > > My understanding is that power runs into similar issues, but I don't > > > know much about power, so I might be entirely wrong :) > > > > Sort of, but not to the same extent, I think. > > I'm curious what are the ramifications of a misguided hotplug on POWER? > Does using F_ACCESS_PLATFORM when it isn't required have any > significant drawbacks, or are you fine to just go with the safe option?
I expect it will have some performance impact, though it shouldn't be
*that* bad, at least if your guest kernel is ddw / large IOMMU window
capable.
Changing the default would require a machine type version bump, of
course.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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