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H A D | Kconfig | 40e27565 Tue Apr 04 21:44:50 CDT 2017 Michael Ellerman <mpe@ellerman.id.au> 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> 40e27565 Tue Apr 04 21:44:50 CDT 2017 Michael Ellerman <mpe@ellerman.id.au> 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>
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