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

David Gibson david at gibson.dropbear.id.au
Thu Sep 28 16:26:05 AEST 2017

On Thu, Sep 28, 2017 at 07:56:01AM +0200, Thomas Huth wrote:
> 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...

Ah, right.

> 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.

Hrm.  Not a lot is occurring to me.  I'm really not too fond of the
approach of the UPDATE_PHANDLE hcall; it's so incomplete.  Not to
mention, I'm not sure what the cost will be of adding an hcall on
every phandle assignment.

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_!
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