Re: [Qemu-ppc] [SLOF] [PATCH v4] board-qemu: add private hcall to inform host on "phandle" update

[Thomas Huth]

On 28.09.2017 06:24, David Gibson wrote:
> On Wed, Sep 27, 2017 at 12:26:09PM +0200, Thomas Huth wrote:
>> On 27.09.2017 11:30, Segher Boessenkool wrote:
>>> On Wed, Sep 27, 2017 at 04:15:43PM +1000, David Gibson wrote:
>>>> 2. At quiesce time, SLOF will linearize it's current version of the DT
>>>>    and submit it to H_UPDATE_DT
>>>
>>> That will work.  It's a big hammer, but that also means it will solve
>>> many related future problems.  I like it :-)
>>
>> ... it's likely just yet another slow-down to the boot process.
>> Linearizing the whole DT in Forth might take a while, I guess.
> 
> Do we have to do it in forth?  We could make a C extension to do this,
> no?

The device tree lives in Forth, so even if you write the code that
creates the FDT in C, you have to call back into Forth for each and
every node and property that you find along the tree. I'm pretty sure it
won't perform extremely fast...

Anyway, to give you a number: The FDT->OF-DT conversion (fdt.fs)
currently takes 350 ms when running SLOF on my Laptop with TCG. I guess
the other way round will be a bit slower (since the device tree lookup
has to search through the Forth dictionaries), so I guess we will have
something around 0.5 seconds in the end. If that slowdown during quiesce
is acceptable, then go for it! If not, it might be better to search a
different solution instead.

 Thomas

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