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PCC regions utilize a mailbox to set/retrieve register values used by the CPPC code. This is fine as long as the operations are infrequent. With the FIE code enabled though the overhead can range from 2-11% of system CPU overhead (ex: as measured by top) on Arm based machines. So, before enabling FIE assure none of the registers used by cppc_get_perf_ctrs() are in the PCC region. Finally, add a module parameter which can override the PCC region detection at boot or module reload. Signed-off-by: Jeremy Linton <jeremy.linton@arm.com> Acked-by: Viresh Kumar <viresh.kumar@linaro.org> Reviewed-by: Ionela Voinescu <ionela.voinescu@arm.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.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.