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>
Currently the idle injection framework uses the play_idle() function
which puts the current CPU in an idle state. The idle state is the
deepest one, as specified by the latency constraint when calling the
subsequent play_idle_precise() function with the INT_MAX.
The idle_injection is used by the cpuidle_cooling device which
computes the idle / run duration to mitigate the temperature by
injecting idle cycles. The cooling device has no control on the depth
of the idle state.
Allow finer control of the idle injection mechanism by allowing to
specify the latency for the idle state. Thus the cooling device has
the ability to have a guarantee on the exit latency of the idle states
it is injecting.
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Amit Kucheria <amit.kucheria@linaro.org>
Link: https://lore.kernel.org/r/20200429103644.5492-1-daniel.lezcano@linaro.org
The resolution of the idle injection is limited to 1ms. If there is
a need for an injection of 1.2 ms, it is not possible.
The idle injection API is not yet used, so it is safe to convert the
existing API to the new time unit instead of adding more functions.
Convert to microsecond in order to use a finer grain time unit when
injecting idle cycles.
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Initially, the cpu_cooling device for ARM was changed by adding a new
policy inserting idle cycles. The intel_powerclamp driver does a
similar action.
Instead of implementing idle injections privately in the cpu_cooling
device, move the idle injection code in a dedicated framework and give
the opportunity to other frameworks to make use of it.
The framework relies on the smpboot kthreads which handles via its
main loop the common code for hotplugging and [un]parking.
This code was previously tested with the cpu cooling device and went
through several iterations. It results now in split code and API
exported in the header file. It was tested with the cpu cooling device
with success.
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
[ rjw: Rewrite of all comments ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
