powerpc/powernv: Always enable SMP when building powernv

The powernv platform supports Power7 and later CPUs, all of which are
multithreaded and multicore.

As such we never build a SMP=n kernel for those machines, other than
possibly for debugging or running in a simulator.

In the debugging case we can get a similar effect by booting with
nr_cpus=1, or there's always the option of building a custom kernel with
SMP hacked out.

For running in simulators the code size reduction from building without
SMP is not particularly important, what matters is the number of
instructions executed. A quick test shows that a SMP=y kernel takes ~6%
more instructions to boot to a shell. Booting with nr_cpus=1 recovers
about half that deficit.

On the flip side, keeping the SMP=n kernel building can be a pain at
times. And although we've mostly kept it building in recent years, no
one is regularly testing that the SMP=n kernel actually boots and works
well on these machines.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/platforms/powernv/Kconfig b/arch/powerpc/platforms/powernv/Kconfig
index 2489805e79f1b424ec489caaa317bb0971f280e9..6a6f4ef46b9e5e0123352e4c1c9f13a7a749c5e6 100644 (file)
--- a/arch/powerpc/platforms/powernv/Kconfig
+++ b/arch/powerpc/platforms/powernv/Kconfig
@@ -21,6 +21,7 @@ config PPC_POWERNV
        select CPU_FREQ_GOV_CONSERVATIVE
        select PPC_DOORBELL
        select MMU_NOTIFIER
+       select FORCE_SMP
        default y
 
 config OPAL_PRD