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The per_cpu_schedule flag is used to move the cpupower process to the cpu
on which we are looking to read the APERF/MPERF registers.
This prevents IPIs from being generated by read_msr()s as we are already
on the cpu of interest.
Ex: If cpupower is running on CPU 0 and we execute
read_msr(20, MSR_APERF, val) then,
read_msr(20, MSR_MPERF, val)
the msr module will generate an IPI from CPU 0 to CPU 20 to query
for the MSR_APERF and then the MSR_MPERF in separate IPIs.
This delay, caused by IPI latency, between reading the APERF and MPERF
registers may cause both of them to go out of sync.
The use of the per_cpu_schedule flag reduces the probability of this
from happening. It comes at the cost of a negligible increase in cpu
consumption caused by the migration of cpupower across each of the
cpus of the system.
Signed-off-by: Janakarajan Natarajan <Janakarajan.Natarajan@amd.com>
Acked-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
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.