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If there are shared processor LPARs, underlying Hypervisor can have more virtual cores to handle than actual physical cores. Starting with Power 9, a big core (aka SMT8 core) has 2 nearly independent thread groups. On a shared processors LPARs, it helps to pack threads to lesser number of cores so that the overall system performance and utilization improves. PowerVM schedules at a big core level. Hence packing to fewer cores helps. Since each thread-group is independent, running threads on both the thread-groups of a SMT8 core, should have a minimal adverse impact in non over provisioned scenarios. These changes in this patchset will not affect in the over provisioned scenario. If there are more threads than SMT domains, then asym_packing will not kick-in For example: Lets says there are two 8-core Shared LPARs that are actually sharing a 8 Core shared physical pool, each running 8 threads each. Then Consolidating 8 threads to 4 cores on each LPAR would help them to perform better. This is because each of the LPAR will get 100% time to run applications and there will no switching required by the Hypervisor. To achieve this, enable SD_ASYM_PACKING flag at CACHE, MC and DIE level when the system is running in shared processor mode and has big cores. Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20231214180720.310852-2-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.