On Fri, 2014-05-23 at 11:53 +0200, Alexander Graf wrote:

On 23.05.14 10:15, Michael Neuling wrote:

quoted

This patch series implements split core mode on POWER8.  This enables u=

p to 4

quoted

subcores per core which can each independently run guests (per guest SP=

Rs like

quoted

SDR1, LPIDR etc are replicated per subcore).  Lots more documentation o=

n this

quoted

feature in the code and commit messages.

Most of this code is in the powernv platform but there's a couple of KV=

M

quoted

specific patches too.

Patch series authored by mpe and me with a few bug fixes from others.

v2:
   There are some minor updates based on comments and I've added the Ac=

ks by

quoted

   Paulus and Alex for the KVM code.

=20
I don't see changelogs inside the individual patches. Please make sure=

=20

to always mention what changed from one version to the next in a=20
particular patch, so that I have the chance to check whether that change=

=20

was good :).

Sure, that was a bit sloppy

Only the last patch was the only one that changed.  I changed the sysfs
file from 600 permissions to 644 so that users can read it more easily
as requested by Joel.

The other change was to fix the possibility of a race when coming out of
nap and checking if we need to split.  This fix was form paulus' (worked
offline).

Also, is there any performance penalty associated with split core mode?=

=20

If not, could we just always default to split-by-4 on POWER8 bare metal?

Yeah, there is a performance hit .  When you are split (ie
subcores_per_core =3D 2 or 4), the core is stuck in SMT8 mode.  So if you
only have 1 thread active (others napped), you won't get the benefit of
ST mode in the core (more register renames per HW thread, more FXUs,
more FPUs etc).

Mikey