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Add architecture specific APIs to update and track thermal pressure on a per CPU basis. A per CPU variable thermal_pressure is introduced to keep track of instantaneous per CPU thermal pressure. Thermal pressure is the delta between maximum capacity and capped capacity due to a thermal event. topology_get_thermal_pressure can be hooked into the scheduler specified arch_scale_thermal_pressure to retrieve instantaneous thermal pressure of a CPU. arch_set_thermal_pressure can be used to update the thermal pressure. Considering topology_get_thermal_pressure reads thermal_pressure and arch_set_thermal_pressure writes into thermal_pressure, one can argue for some sort of locking mechanism to avoid a stale value. But considering topology_get_thermal_pressure can be called from a system critical path like scheduler tick function, a locking mechanism is not ideal. This means that it is possible the thermal_pressure value used to calculate average thermal pressure for a CPU can be stale for up to 1 tick period. Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lkml.kernel.org/r/20200222005213.3873-4-thara.gopinath@linaro.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.