> On Sun, Feb 20, 2000 at 12:42:14PM +1100, Patryk Zadarnowski wrote:
> > One more thing about GPTs (I thought I'll leave that till last. ;)
> > Jochen Liedtke holds a German patent on them, although he will
> > probably be fairly easily convinced to give FreeBSD rights to use
> > them. I'll be happy to ask (if we're interested.)
>
> It looks like the hardware has to implement GPTs and know how to
> walk them. How can FreeBSD use them without hardware support ?
No it doesn't. We've got software GPT implementations for both MIPS64 and
Alpha, and they're both peform very well in our somewhat hostile SASOS
conditions. I'm not sure why you think that a hardware walk is necessary: the
only reason why IA-64 walks VPHT in hardware *at all* is to minimize the
impact on the pipeline and improve ILP: remember that the IA-64 hardware walk
is *advisory* -- that is, the OS still must supply software TLB refill
handlers, even if it uses a linear page table. Specifically, even though the
simulator may not display that behaviour, Itanium aborts the VPHT walk early
in quite a few cornel cases, even if completing the walk would avoid a TLB
miss.
Pat.
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