Re: [Qemu-ppc] [PATCH] powerpc iommu: enable multiple TCE requests

[Paolo Bonzini]

Il 20/08/2013 11:26, Benjamin Herrenschmidt ha scritto:
> On Tue, 2013-08-20 at 11:22 +0200, Paolo Bonzini wrote:
>>
>> Uhm... I thought Alex and I were the one who proposed the simple things.
>>  You _will_ need to do the complicated stuff sooner or later, but it's
>> probably early enough now to ignore it.
>>
>> And I'm not saying this out of love for big cathedrals, but out of
>> lessons we learned the hard way for x86 (where we haven't gotten
>> everything right yet, either).
> 
> I suppose if RH is going to deploy 3.10 and we aren't going to backport
> the multitce patches then there *might* be a case for supporting that
> combo specifically... but it's going to be that bad every time we add
> a new feature with a kernel counter part or start adding the gazillion
> little bits of PAPR that we are still missing ?

Yes. :(

Unless you consider pSeries KVM not mature enough to provide a guest ABI
(basically supporting live migration only between identical kernels and
QEMUs).  It would make some sense, for example (mutatis mutandis) Red
Hat has a kernel ABI for the "regular" RHEL kernel, but not for the
"real-time" RHEL kernel.

Paolo