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The powercap/idle_inject core uses play_idle_precise() to inject idle time. But play_idle_precise() can't ensure that the CPU is fully idle for the specified duration because of wakeups due to interrupts. To compensate for the reduced idle time due to these wakes, the caller can adjust requested idle time for the next cycle. The goal of idle injection is to keep system at some idle percent on average, so this is fine to overshoot or undershoot instantaneous idle times. The idle inject core provides an interface idle_inject_set_duration() to set idle and runtime duration. Some architectures provide interface to get actual idle time observed by the hardware. So, the effective idle percent can be adjusted using the hardware feedback. For example, Intel CPUs provides package idle counters, which is currently used by Intel powerclamp driver to readjust runtime duration. When the caller's desired idle time over a period is less or greater than the actual CPU idle time observed by the hardware, caller can readjust idle and runtime duration for the next cycle. The only way this can be done currently is by monitoring hardware idle time from a different software thread and readjust idle and runtime duration using idle_inject_set_duration(). This can be avoided by adding a callback which callers can register and readjust from this callback function. Add a capability to register an optional update() callback, which can be called from the idle inject core before waking up CPUs for idle injection. This callback can be registered via a new interface: idle_inject_register_full(). During this process of constantly adjusting idle and runtime duration there can be some cases where actual idle time is more than the desired. In this case idle inject can be skipped for a cycle. If update() callback returns false, then the idle inject core skips waking up CPUs for the idle injection. Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> |
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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.