Re: [Qemu-devel] [PATCHv2 00/10] Clean up page size handling for ppc 64-bit hash MMUs with TCG

[David Gibson]

On Thu, Jan 28, 2016 at 09:44:53PM +0100, Alexander Graf wrote:
> 
> 
> On 01/27/2016 11:13 AM, 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.
> >
> >For a simple benchmark I timed fully booting then cleanly shutting
> >down a TCG guest (RHEL7.2 userspace with a recent upstream kernel).
> >Repeated 5 times on the current master branch, my current ppc-for-2.6
> >branch and this branch.  It looks like it improves speed, although the
> >difference is pretty much negligible:
> >
> >master:              2m25 2m28 2m26 2m26 2m26
> >ppc-for-2.6:    2m26 2m25 2m26 2m27 2m25
> >this series:    2m20 2m23 2m23 2m25 2m21
> >
> >Please review, and I'll fold into ppc-for-2.6 for my next pull.
> >
> >Changes since v1:
> >   * Fix a couple of simple but serious bugs in logic
> >   * Did some rudimentary benchmarking
> >Changes since RFC:
> >   * Moved lookup of SLB encodings table from SLB lookup time to SLB
> >       store time
> 
> LGTM, apart from the comments that people already made. Please also provide
> changelogs in the individual patch files next time - it makes it easier for
> people who just try to see what changed from one version to another ;).
> 
> Reviewed-by: Alexander Graf <address@hidden>

Thanks, I've merged to ppc-for-2.6.

> Also, please just double sanity check that the code after your conversion
> still works well on 32bit hosts ;). I suppose you have a 32bit build
> environment by now, so that should be quite easy to pull off.

Yeah, will do.  I'm still pretty pissed that glib breaks the multiarch
build, which should be straightforward, but I have something workable.

-- 
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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