Some partners have value-adds based on aosp/540066, which cannot be
carried in ACK in its entirety as it no longer makes sense as-is (the
select_idle_capacity() rework upstream solved the issue differently).
It seems that those partners do not actually need the wake-wide tweaks,
they only need to access the wake_q length for wake-up balance. To
support this, add minimal tracking to the wake_q infrastructure in the
core kernel, but do that by adding a pointer to the wake_q_head to
task_struct directly to not litter all sched classes with an additional
sibling_count_hint argument to the select_task_rq callbacks.
Modules needing to access the wake_q length can do so by dereferencing
p->wake_q_head in the wake-up path when it is non-NULL.
Bug: 173981591
Signed-off-by: Quentin Perret <qperret@google.com>
Change-Id: I9a98167face92e70aba847d9f04d0c216065478c
1a29b384b0