[Skiboot] [RFC PATCH] Use two VSX registers to do initial copy of skiboot

Michael Neuling mikey at neuling.org
Fri May 22 14:15:52 AEST 2015

On Fri, 2015-05-22 at 00:07 +1000, Stewart Smith wrote:
> Benjamin Herrenschmidt <benh at kernel.crashing.org> writes:
> > On Thu, 2015-05-21 at 18:40 +1000, Stewart Smith wrote:
> >> Note my awful fiddling of MSR so that I can use VSX registers :)
> >
> > Is this really worth it ? :-) I like being conservative in that
> > code...
> Maybe, maybe not... Mikey is playing with some simulator foo and wanting
> to get cycle count down. Of course, if you change the load location then
> you avoid it, but then you also execute a bit differently than on real
> hardware.

So on this... If we can assume that memory is zero, we can save a lot of
cycles with not having to zero out some stuff (console, cpu stacks and
trace buffer in particular).  I can get the number of instructions
required to boot in sim down from 15M to 600K (ie 20x faster).  

benh, can we use the ipl-params/ipl-params/cec-major-type property to
mark "cold" boots as having zeroed memory, and hence skip some of these?
I'd like to do this at run time, rather than compile time .


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