Commit a2e90611 authored by Vincent Guittot's avatar Vincent Guittot Committed by Peter Zijlstra
Browse files

sched/fair: Remove capacity inversion detection 



Remove the capacity inversion detection which is now handled by
util_fits_cpu() returning -1 when we need to continue to look for a
potential CPU with better performance.

This ends up almost reverting patches below except for some comments:
commit da07d2f9 ("sched/fair: Fixes for capacity inversion detection")
commit aa69c36f ("sched/fair: Consider capacity inversion in util_fits_cpu()")
commit 44c7b80b ("sched/fair: Detect capacity inversion")

Signed-off-by: default avatarVincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230201143628.270912-3-vincent.guittot@linaro.org
parent e5ed0550

kernel/sched/fair.c

+5 −79
Original line number Diff line number Diff line
@@ -4476,17 +4476,9 @@ static inline int util_fits_cpu(unsigned long util, 
	 *

	 * For uclamp_max, we can tolerate a drop in performance level as the

	 * goal is to cap the task. So it's okay if it's getting less.

	 *

	 * In case of capacity inversion we should honour the inverted capacity

	 * for both uclamp_min and uclamp_max all the time.

	 */

	capacity_orig = cpu_in_capacity_inversion(cpu);

	if (capacity_orig) {

		capacity_orig_thermal = capacity_orig;

	} else {

	capacity_orig = capacity_orig_of(cpu);

	capacity_orig_thermal = capacity_orig - arch_scale_thermal_pressure(cpu);

	}



	/*

	 * We want to force a task to fit a cpu as implied by uclamp_max.
@@ -9027,82 +9019,16 @@ static unsigned long scale_rt_capacity(int cpu) 


static void update_cpu_capacity(struct sched_domain *sd, int cpu)

{

	unsigned long capacity_orig = arch_scale_cpu_capacity(cpu);

	unsigned long capacity = scale_rt_capacity(cpu);

	struct sched_group *sdg = sd->groups;

	struct rq *rq = cpu_rq(cpu);



	rq->cpu_capacity_orig = capacity_orig;

	cpu_rq(cpu)->cpu_capacity_orig = arch_scale_cpu_capacity(cpu);



	if (!capacity)

		capacity = 1;



	rq->cpu_capacity = capacity;



	/*

	 * Detect if the performance domain is in capacity inversion state.

	 *

	 * Capacity inversion happens when another perf domain with equal or

	 * lower capacity_orig_of() ends up having higher capacity than this

	 * domain after subtracting thermal pressure.

	 *

	 * We only take into account thermal pressure in this detection as it's

	 * the only metric that actually results in *real* reduction of

	 * capacity due to performance points (OPPs) being dropped/become

	 * unreachable due to thermal throttling.

	 *

	 * We assume:

	 *   * That all cpus in a perf domain have the same capacity_orig

	 *     (same uArch).

	 *   * Thermal pressure will impact all cpus in this perf domain

	 *     equally.

	 */

	if (sched_energy_enabled()) {

		unsigned long inv_cap = capacity_orig - thermal_load_avg(rq);

		struct perf_domain *pd;



		rcu_read_lock();



		pd = rcu_dereference(rq->rd->pd);

		rq->cpu_capacity_inverted = 0;



		for (; pd; pd = pd->next) {

			struct cpumask *pd_span = perf_domain_span(pd);

			unsigned long pd_cap_orig, pd_cap;



			/* We can't be inverted against our own pd */

			if (cpumask_test_cpu(cpu_of(rq), pd_span))

				continue;



			cpu = cpumask_any(pd_span);

			pd_cap_orig = arch_scale_cpu_capacity(cpu);



			if (capacity_orig < pd_cap_orig)

				continue;



			/*

			 * handle the case of multiple perf domains have the

			 * same capacity_orig but one of them is under higher

			 * thermal pressure. We record it as capacity

			 * inversion.

			 */

			if (capacity_orig == pd_cap_orig) {

				pd_cap = pd_cap_orig - thermal_load_avg(cpu_rq(cpu));



				if (pd_cap > inv_cap) {

					rq->cpu_capacity_inverted = inv_cap;

					break;

				}

			} else if (pd_cap_orig > inv_cap) {

				rq->cpu_capacity_inverted = inv_cap;

				break;

			}

		}



		rcu_read_unlock();

	}



	trace_sched_cpu_capacity_tp(rq);

	cpu_rq(cpu)->cpu_capacity = capacity;

	trace_sched_cpu_capacity_tp(cpu_rq(cpu));



	sdg->sgc->capacity = capacity;

	sdg->sgc->min_capacity = capacity;

kernel/sched/sched.h

+0 −19
Original line number Diff line number Diff line
@@ -1044,7 +1044,6 @@ struct rq { 


	unsigned long		cpu_capacity;

	unsigned long		cpu_capacity_orig;

	unsigned long		cpu_capacity_inverted;



	struct balance_callback *balance_callback;
@@ -2899,24 +2898,6 @@ static inline unsigned long capacity_orig_of(int cpu) 
	return cpu_rq(cpu)->cpu_capacity_orig;

}



/*

 * Returns inverted capacity if the CPU is in capacity inversion state.

 * 0 otherwise.

 *

 * Capacity inversion detection only considers thermal impact where actual

 * performance points (OPPs) gets dropped.

 *

 * Capacity inversion state happens when another performance domain that has

 * equal or lower capacity_orig_of() becomes effectively larger than the perf

 * domain this CPU belongs to due to thermal pressure throttling it hard.

 *

 * See comment in update_cpu_capacity().

 */

static inline unsigned long cpu_in_capacity_inversion(int cpu)

{

	return cpu_rq(cpu)->cpu_capacity_inverted;

}



/**

 * enum cpu_util_type - CPU utilization type

 * @FREQUENCY_UTIL:	Utilization used to select frequency