Re: [Qemu-devel] [PATCH qemu] spapr: Render full FDT on ibm, client-architecture-support

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 26/08/2019 17:44, David Gibson wrote:
> On Mon, Aug 26, 2019 at 02:31:26PM +1000, Alexey Kardashevskiy wrote:
>> The ibm,client-architecture-support call is a way for the guest to
>> negotiate capabilities with a hypervisor. It is implemented as:
>> - the guest calls SLOF via client interface;
>> - SLOF calls QEMU (H_CAS hypercall) with an options vector from the guest;
>> - QEMU returns a device tree diff (which uses FDT format with
>> an additional header before it);
>> - SLOF walks through the partial diff tree and updates its internal tree
>> with the values from the diff.
>>
>> This changes QEMU to simply re-render the entire tree and send it as
>> an update. SLOF can handle this already mostly, [1] is needed before this
>> can be applied.
>>
>> The benefit is reduced code size as there is no need for another set of
>> DT rendering helpers such as spapr_fixup_cpu_dt().
>>
>> The downside is that the updates are bigger now (as they include all
>> nodes and properties) but the difference on a '-smp 256,threads=1' system
>> before/after is 2.35s vs. 2.5s.
>>
>> While at this, add a missing g_free(fdt) if the resulting tree is bigger
>> than the space allocated by SLOF. Also, store the resulting tree in
>> the spapr machine to have the latest valid FDT copy possible (this should
>> not matter much as H_UPDATE_DT happens right after that but nevertheless).
>>
>> [1] https://patchwork.ozlabs.org/patch/1152915/
>>
>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> 
> Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
> 
> Can you wrap that up with the SLOF update in a pull request for me?


Yup, I'll just wait a little bit more for replies about the RTAS log 
extension patch. Cheers,



-- 
Alexey