sched/cache: Prioritize tasks preferring destination LLC during balancing

sched/cache: Prioritize tasks preferring destination LLC during balancing

During LLC load balancing, first check for tasks that prefer the
destination LLC and balance them to it before others.

Mark source sched groups containing tasks preferring non local LLCs
with the group_llc_balance flag. This ensures the load balancer later
pulls or pushes these tasks toward their preferred LLCs.
The priority of group_llc_balance is lower than that of group_overloaded
and higher than that of all other group types. This is because
group_llc_balance may exacerbate load imbalance, and if the LLC balancing
attempt fails, the nr_balance_failed mechanism will trigger other group
types to rebalance the load.

The load balancer selects the busiest sched_group and migrates tasks
to less busy groups to distribute load across CPUs.

With cache-aware scheduling enabled, the busiest sched_group is
the one with most tasks preferring the destination LLC. If
the group has the llc_balance flag set, cache aware load balancing is
triggered.

Introduce the helper function update_llc_busiest() to identify the
sched_group with the most tasks preferring the destination LLC.

Suggested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Suggested-by: Madadi Vineeth Reddy <vineethr@linux.ibm.com>
Co-developed-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/baa458f45eab3f602af090c6d6af63dc864f5ec6.1775065312.git.tim.c.chen@linux.intel.com