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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>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.