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

[David Gibson]

On Thu, Sep 28, 2017 at 03:40:09AM -0500, Segher Boessenkool wrote:
> 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:
> > >> ... 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.
> 
> Converting the device tree to an FDT should take about the same time
> as "dev / ls".  How long does that take?

Actually, I doubt that, since I suspect dev / ls will be limited by
the actual output - either slow serial or quasi-serial or slow(ish)
rendering of characters on a framebuffer.

> 
> There are no dictionary lookups needed.
> 
> 
> Segher
> 

-- 
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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