ANDROID: sched/fair: Bias EAS placement for latency
Add to find_energy_efficient_cpu() a latency sensitive case which mimics
what was done for prefer-idle in android-4.19 and before (see [1] for
reference).
This isn't strictly equivalent to the legacy algorithm but comes real
close, and isn't very invasive. Overall, the idea is to select the
biggest idle CPU we can find for latency-sensitive boosted tasks, and
the smallest CPU where the can fit for latency-sensitive non-boosted
tasks.
The main differences with the legacy behaviour are the following:
1. the policy for 'prefer idle' when there isn't a single idle CPU in
the system is simpler now. We just pick the CPU with the highest
spare capacity;
2. the cstate awareness is implemented by minimizing the exit latency
rather than the idle state index. This is how it is done in the slow
path (find_idlest_group_cpu()), it doesn't require us to keep hooks
into CPUIdle, and should actually be better because what we want is
a CPU that can wake up quickly;
3. non-latency-sensitive tasks just use the standard mainline
energy-aware wake-up path, which decides the placement using the
Energy Model;
4. the 'boosted' and 'latency_sensitive' attributes of a task come from
util_clamp (which now replaces schedtune).
[1] https://android.googlesource.com/kernel/common.git/+/c27c56105dcaaae54ecc39ef33fbfac87a1486fc
Change-Id: Ia58516906e9cb5abe08385a8cd088097043d8703
Signed-off-by: Quentin Perret <[email protected]>
1 file changed
