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Anton Blanchard reported that his 4096 vcpu KVM guest took around 30 minutes to boot. He also analyzed it to the time taken to iterate while setting the cpu_core_mask. Further analysis shows that cpu_core_mask and cpu_cpu_mask for any CPU would be equal on Power. However updating cpu_core_mask took forever to update as its a per cpu cpumask variable. Instead cpu_cpu_mask was a per NODE /per DIE cpumask that was shared by all the respective CPUs. Also cpu_cpu_mask is needed from a scheduler perspective. However cpu_core_map is an exported symbol. Hence stop updating cpu_core_map and make it point to cpu_cpu_mask. Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com> Tested-by: Satheesh Rajendran <sathnaga@linux.vnet.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20200921095653.9701-3-srikar@linux.vnet.ibm.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
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.