Re: [Qemu-ppc] [PATCH 00/10] Clean up page size handling for ppc 64-bit hash MMUs with TCG

[David Gibson]

On Mon, Jan 25, 2016 at 09:36:40PM +0100, Alexander Graf wrote:
> 
> 
> On 01/25/2016 12:10 PM, David Gibson wrote:
> >On Mon, Jan 25, 2016 at 04:15:42PM +1100, David Gibson wrote:
> >>Encoding of page sizes on 64-bit hash MMUs for Power is rather arcane,
> >>involving control bits in both the SLB and HPTE.  At present we
> >>support a few of the options, but far fewer than real hardware.
> >>
> >>We're able to get away with that in practice, because guests use a
> >>device tree property to determine which page sizes are available and
> >>we are setting that to match.  However, the fact that the actual code
> >>doesn't necessarily what we put into the table of available page sizes
> >>is another ugliness.
> >>
> >>This series makes a number of cleanups to the page size handling.  The
> >>upshot is that afterwards the softmmu code operates off the same page
> >>size encoding table that is advertised to the guests, ensuring that
> >>they will be in sync.
> >>
> >>Finally, we extend the table of allowed sizes for POWER7 and POWER8 to
> >>include the options allowed in hardware (including MPSS).  We can fix
> >>other hash MMU based CPUs in future if anyone cares enough.
> >>
> >>Please review, and I'll fold into ppc-for-2.6 for my next pull.
> >Bother, somehow missed a serious bug in here that's causing
> >oops-on-boot.  Sorry, still tracking it down.
> 
> I still have no idea where your bug is (bisect probably should get you there
> pretty quick),

Alas, no, because the bug only triggers once all the page sizes are
added for POWER8 in the last patch.

Luckily I found it anyway (see earlier reply).

> but the overall concept sounds very reasonable to me. Please
> benchmark performance before and after in the next cover letter also
> :)

Hrm.. as always the question is what benchmark?

> 
> Reviewed-by: Alexander Graf <address@hidden>
> 
> Alex
> 

-- 
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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