Re: PPC440 tlbwe

[Nicholas Piggin]

On Wed Oct 25, 2023 at 2:01 AM AEST, BALATON Zoltan wrote:
> On Wed, 11 Oct 2023, Nicholas Piggin wrote:
> > On Tue Oct 10, 2023 at 10:41 PM AEST, BALATON Zoltan wrote:
> >> Hello,
> >>
> >> I have a question about tlbwe emulation in TCG for PPC440. This seems to
> >> be implemented in mmu_helper.c::helper_440_tlbwe which calls tlb_flush a
> >> lot flushing all TLB entries. This causes a big performance hit with
> >> sam460ex running AmigaOS which seems to do tlbwe on every task or context
> >> switch so it runs much slower than on other machines with a G4 CPU
> >> (pegasos2 and amigaone we also emulate) that use hardware TLB which does
> >> not have such problem in TCG. Even the embedded TLB emulation has 3
> >> versions for 40x, 440 and BookE 2.06 (I think that's e500) and at least
> >> the booke206 version uses flush_page instead of flushing everything. I
> >> don't know much about this so is there somebody with better understanding
> >> of this who can have a look at it and see if it can be optimised to
> >> resolve this problem or give some advice?
> >
> > It looks like 440 might be able to use the same page flushing as 4xx.
> >
> > This patch is only compile tested and I don't know the book E TLB stuff
> > too well but it may give you a starting point.
>
> A few more people gave this some testing and it seems to work and found no 
> breakage so far. Do you plan to make it a porper patch and merge it 
> sometimes?

Performance is improved do you think? I can give it a try. I may try to
do the fix patches separately ahead of the performance patch. It would
be nice if those could be confirmed to fix a problem, but understand
it can be difficult to set up and hit TLB bugs.

Thanks,
Nick