[v2,2/2] sched_ext: Add cpuperf support

--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -197,8 +197,10 @@  unsigned long sugov_effective_cpu_perf(i
 
 static void sugov_get_util(struct sugov_cpu *sg_cpu, unsigned long boost)
 {
-	unsigned long min, max, util = cpu_util_cfs_boost(sg_cpu->cpu);
+	unsigned long min, max, util = scx_cpuperf_target(sg_cpu->cpu);
 
+	if (!scx_switched_all())
+		util += cpu_util_cfs_boost(sg_cpu->cpu);
 	util = effective_cpu_util(sg_cpu->cpu, util, &min, &max);
 	util = max(util, boost);
 	sg_cpu->bw_min = min;
@@ -330,6 +332,14 @@  static bool sugov_hold_freq(struct sugov
 	unsigned long idle_calls;
 	bool ret;
 
+	/*
+	 * The heuristics in this function is for the fair class. For SCX, the
+	 * performance target comes directly from the BPF scheduler. Let's just
+	 * follow it.
+	 */
+	if (scx_switched_all())
+		return false;
+
 	/* if capped by uclamp_max, always update to be in compliance */
 	if (uclamp_rq_is_capped(cpu_rq(sg_cpu->cpu)))
 		return false;
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -16,6 +16,8 @@  enum scx_consts {
 	SCX_EXIT_BT_LEN			= 64,
 	SCX_EXIT_MSG_LEN		= 1024,
 	SCX_EXIT_DUMP_DFL_LEN		= 32768,
+
+	SCX_CPUPERF_ONE			= SCHED_CAPACITY_SCALE,
 };
 
 enum scx_exit_kind {
@@ -3520,7 +3522,7 @@  DEFINE_SCHED_CLASS(ext) = {
 	.update_curr		= update_curr_scx,
 
 #ifdef CONFIG_UCLAMP_TASK
-	.uclamp_enabled		= 0,
+	.uclamp_enabled		= 1,
 #endif
 };
 
@@ -4393,7 +4395,7 @@  static int scx_ops_enable(struct sched_e
 	struct scx_task_iter sti;
 	struct task_struct *p;
 	unsigned long timeout;
-	int i, ret;
+	int i, cpu, ret;
 
 	mutex_lock(&scx_ops_enable_mutex);
 
@@ -4442,6 +4444,9 @@  static int scx_ops_enable(struct sched_e
 
 	atomic_long_set(&scx_nr_rejected, 0);
 
+	for_each_possible_cpu(cpu)
+		cpu_rq(cpu)->scx.cpuperf_target = SCX_CPUPERF_ONE;
+
 	/*
 	 * Keep CPUs stable during enable so that the BPF scheduler can track
 	 * online CPUs by watching ->on/offline_cpu() after ->init().
@@ -5836,6 +5841,77 @@  __bpf_kfunc void scx_bpf_dump_bstr(char
 }
 
 /**
+ * scx_bpf_cpuperf_cap - Query the maximum relative capacity of a CPU
+ * @cpu: CPU of interest
+ *
+ * Return the maximum relative capacity of @cpu in relation to the most
+ * performant CPU in the system. The return value is in the range [1,
+ * %SCX_CPUPERF_ONE]. See scx_bpf_cpuperf_cur().
+ */
+__bpf_kfunc u32 scx_bpf_cpuperf_cap(s32 cpu)
+{
+	if (ops_cpu_valid(cpu, NULL))
+		return arch_scale_cpu_capacity(cpu);
+	else
+		return SCX_CPUPERF_ONE;
+}
+
+/**
+ * scx_bpf_cpuperf_cur - Query the current relative performance of a CPU
+ * @cpu: CPU of interest
+ *
+ * Return the current relative performance of @cpu in relation to its maximum.
+ * The return value is in the range [1, %SCX_CPUPERF_ONE].
+ *
+ * The current performance level of a CPU in relation to the maximum performance
+ * available in the system can be calculated as follows:
+ *
+ *   scx_bpf_cpuperf_cap() * scx_bpf_cpuperf_cur() / %SCX_CPUPERF_ONE
+ *
+ * The result is in the range [1, %SCX_CPUPERF_ONE].
+ */
+__bpf_kfunc u32 scx_bpf_cpuperf_cur(s32 cpu)
+{
+	if (ops_cpu_valid(cpu, NULL))
+		return arch_scale_freq_capacity(cpu);
+	else
+		return SCX_CPUPERF_ONE;
+}
+
+/**
+ * scx_bpf_cpuperf_set - Set the relative performance target of a CPU
+ * @cpu: CPU of interest
+ * @perf: target performance level [0, %SCX_CPUPERF_ONE]
+ * @flags: %SCX_CPUPERF_* flags
+ *
+ * Set the target performance level of @cpu to @perf. @perf is in linear
+ * relative scale between 0 and %SCX_CPUPERF_ONE. This determines how the
+ * schedutil cpufreq governor chooses the target frequency.
+ *
+ * The actual performance level chosen, CPU grouping, and the overhead and
+ * latency of the operations are dependent on the hardware and cpufreq driver in
+ * use. Consult hardware and cpufreq documentation for more information. The
+ * current performance level can be monitored using scx_bpf_cpuperf_cur().
+ */
+__bpf_kfunc void scx_bpf_cpuperf_set(u32 cpu, u32 perf)
+{
+	if (unlikely(perf > SCX_CPUPERF_ONE)) {
+		scx_ops_error("Invalid cpuperf target %u for CPU %d", perf, cpu);
+		return;
+	}
+
+	if (ops_cpu_valid(cpu, NULL)) {
+		struct rq *rq = cpu_rq(cpu);
+
+		rq->scx.cpuperf_target = perf;
+
+		rcu_read_lock_sched_notrace();
+		cpufreq_update_util(cpu_rq(cpu), 0);
+		rcu_read_unlock_sched_notrace();
+	}
+}
+
+/**
  * scx_bpf_nr_cpu_ids - Return the number of possible CPU IDs
  *
  * All valid CPU IDs in the system are smaller than the returned value.
@@ -6045,6 +6121,9 @@  BTF_ID_FLAGS(func, scx_bpf_destroy_dsq)
 BTF_ID_FLAGS(func, scx_bpf_exit_bstr, KF_TRUSTED_ARGS)
 BTF_ID_FLAGS(func, scx_bpf_error_bstr, KF_TRUSTED_ARGS)
 BTF_ID_FLAGS(func, scx_bpf_dump_bstr, KF_TRUSTED_ARGS)
+BTF_ID_FLAGS(func, scx_bpf_cpuperf_cap)
+BTF_ID_FLAGS(func, scx_bpf_cpuperf_cur)
+BTF_ID_FLAGS(func, scx_bpf_cpuperf_set)
 BTF_ID_FLAGS(func, scx_bpf_nr_cpu_ids)
 BTF_ID_FLAGS(func, scx_bpf_get_possible_cpumask, KF_ACQUIRE)
 BTF_ID_FLAGS(func, scx_bpf_get_online_cpumask, KF_ACQUIRE)
--- a/kernel/sched/ext.h
+++ b/kernel/sched/ext.h
@@ -48,6 +48,14 @@  int scx_check_setscheduler(struct task_s
 bool task_should_scx(struct task_struct *p);
 void init_sched_ext_class(void);
 
+static inline u32 scx_cpuperf_target(s32 cpu)
+{
+	if (scx_enabled())
+		return cpu_rq(cpu)->scx.cpuperf_target;
+	else
+		return 0;
+}
+
 static inline const struct sched_class *next_active_class(const struct sched_class *class)
 {
 	class++;
@@ -89,6 +97,7 @@  static inline void scx_pre_fork(struct t
 static inline int scx_fork(struct task_struct *p) { return 0; }
 static inline void scx_post_fork(struct task_struct *p) {}
 static inline void scx_cancel_fork(struct task_struct *p) {}
+static inline u32 scx_cpuperf_target(s32 cpu) { return 0; }
 static inline bool scx_can_stop_tick(struct rq *rq) { return true; }
 static inline void scx_rq_activate(struct rq *rq) {}
 static inline void scx_rq_deactivate(struct rq *rq) {}
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -743,6 +743,7 @@  struct scx_rq {
 	u64			extra_enq_flags;	/* see move_task_to_local_dsq() */
 	u32			nr_running;
 	u32			flags;
+	u32			cpuperf_target;		/* [0, SCHED_CAPACITY_SCALE] */
 	bool			cpu_released;
 	cpumask_var_t		cpus_to_kick;
 	cpumask_var_t		cpus_to_kick_if_idle;
--- a/tools/sched_ext/include/scx/common.bpf.h
+++ b/tools/sched_ext/include/scx/common.bpf.h
@@ -42,6 +42,9 @@  void scx_bpf_destroy_dsq(u64 dsq_id) __k
 void scx_bpf_exit_bstr(s64 exit_code, char *fmt, unsigned long long *data, u32 data__sz) __ksym __weak;
 void scx_bpf_error_bstr(char *fmt, unsigned long long *data, u32 data_len) __ksym;
 void scx_bpf_dump_bstr(char *fmt, unsigned long long *data, u32 data_len) __ksym __weak;
+u32 scx_bpf_cpuperf_cap(s32 cpu) __ksym __weak;
+u32 scx_bpf_cpuperf_cur(s32 cpu) __ksym __weak;
+void scx_bpf_cpuperf_set(s32 cpu, u32 perf) __ksym __weak;
 u32 scx_bpf_nr_cpu_ids(void) __ksym __weak;
 const struct cpumask *scx_bpf_get_possible_cpumask(void) __ksym __weak;
 const struct cpumask *scx_bpf_get_online_cpumask(void) __ksym __weak;
--- a/tools/sched_ext/scx_qmap.bpf.c
+++ b/tools/sched_ext/scx_qmap.bpf.c
@@ -69,6 +69,18 @@  struct {
 };
 
 /*
+ * If enabled, CPU performance target is set according to the queue index
+ * according to the following table.
+ */
+static const u32 qidx_to_cpuperf_target[] = {
+	[0] = SCX_CPUPERF_ONE * 0 / 4,
+	[1] = SCX_CPUPERF_ONE * 1 / 4,
+	[2] = SCX_CPUPERF_ONE * 2 / 4,
+	[3] = SCX_CPUPERF_ONE * 3 / 4,
+	[4] = SCX_CPUPERF_ONE * 4 / 4,
+};
+
+/*
  * Per-queue sequence numbers to implement core-sched ordering.
  *
  * Tail seq is assigned to each queued task and incremented. Head seq tracks the
@@ -95,6 +107,8 @@  struct {
 struct cpu_ctx {
 	u64	dsp_idx;	/* dispatch index */
 	u64	dsp_cnt;	/* remaining count */
+	u32	avg_weight;
+	u32	cpuperf_target;
 };
 
 struct {
@@ -107,6 +121,8 @@  struct {
 /* Statistics */
 u64 nr_enqueued, nr_dispatched, nr_reenqueued, nr_dequeued;
 u64 nr_core_sched_execed;
+u32 cpuperf_min, cpuperf_avg, cpuperf_max;
+u32 cpuperf_target_min, cpuperf_target_avg, cpuperf_target_max;
 
 s32 BPF_STRUCT_OPS(qmap_select_cpu, struct task_struct *p,
 		   s32 prev_cpu, u64 wake_flags)
@@ -313,6 +329,29 @@  void BPF_STRUCT_OPS(qmap_dispatch, s32 c
 	}
 }
 
+void BPF_STRUCT_OPS(qmap_tick, struct task_struct *p)
+{
+	struct cpu_ctx *cpuc;
+	u32 zero = 0;
+	int idx;
+
+	if (!(cpuc = bpf_map_lookup_elem(&cpu_ctx_stor, &zero))) {
+		scx_bpf_error("failed to look up cpu_ctx");
+		return;
+	}
+
+	/*
+	 * Use the running avg of weights to select the target cpuperf level.
+	 * This is a demonstration of the cpuperf feature rather than a
+	 * practical strategy to regulate CPU frequency.
+	 */
+	cpuc->avg_weight = cpuc->avg_weight * 3 / 4 + p->scx.weight / 4;
+	idx = weight_to_idx(cpuc->avg_weight);
+	cpuc->cpuperf_target = qidx_to_cpuperf_target[idx];
+
+	scx_bpf_cpuperf_set(scx_bpf_task_cpu(p), cpuc->cpuperf_target);
+}
+
 /*
  * The distance from the head of the queue scaled by the weight of the queue.
  * The lower the number, the older the task and the higher the priority.
@@ -422,8 +461,9 @@  void BPF_STRUCT_OPS(qmap_dump_cpu, struc
 	if (!(cpuc = bpf_map_lookup_percpu_elem(&cpu_ctx_stor, &zero, cpu)))
 		return;
 
-	scx_bpf_dump("QMAP: dsp_idx=%llu dsp_cnt=%llu",
-		     cpuc->dsp_idx, cpuc->dsp_cnt);
+	scx_bpf_dump("QMAP: dsp_idx=%llu dsp_cnt=%llu avg_weight=%u cpuperf_target=%u",
+		     cpuc->dsp_idx, cpuc->dsp_cnt, cpuc->avg_weight,
+		     cpuc->cpuperf_target);
 }
 
 void BPF_STRUCT_OPS(qmap_dump_task, struct scx_dump_ctx *dctx, struct task_struct *p)
@@ -492,11 +532,106 @@  void BPF_STRUCT_OPS(qmap_cpu_offline, s3
 	print_cpus();
 }
 
+struct monitor_timer {
+	struct bpf_timer timer;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, u32);
+	__type(value, struct monitor_timer);
+} monitor_timer SEC(".maps");
+
+/*
+ * Print out the min, avg and max performance levels of CPUs every second to
+ * demonstrate the cpuperf interface.
+ */
+static void monitor_cpuperf(void)
+{
+	u32 zero = 0, nr_cpu_ids;
+	u64 cap_sum = 0, cur_sum = 0, cur_min = SCX_CPUPERF_ONE, cur_max = 0;
+	u64 target_sum = 0, target_min = SCX_CPUPERF_ONE, target_max = 0;
+	const struct cpumask *online;
+	int i, nr_online_cpus = 0;
+
+	nr_cpu_ids = scx_bpf_nr_cpu_ids();
+	online = scx_bpf_get_online_cpumask();
+
+	bpf_for(i, 0, nr_cpu_ids) {
+		struct cpu_ctx *cpuc;
+		u32 cap, cur;
+
+		if (!bpf_cpumask_test_cpu(i, online))
+			continue;
+		nr_online_cpus++;
+
+		/* collect the capacity and current cpuperf */
+		cap = scx_bpf_cpuperf_cap(i);
+		cur = scx_bpf_cpuperf_cur(i);
+
+		cur_min = cur < cur_min ? cur : cur_min;
+		cur_max = cur > cur_max ? cur : cur_max;
+
+		/*
+		 * $cur is relative to $cap. Scale it down accordingly so that
+		 * it's in the same scale as other CPUs and $cur_sum/$cap_sum
+		 * makes sense.
+		 */
+		cur_sum += cur * cap / SCX_CPUPERF_ONE;
+		cap_sum += cap;
+
+		if (!(cpuc = bpf_map_lookup_percpu_elem(&cpu_ctx_stor, &zero, i))) {
+			scx_bpf_error("failed to look up cpu_ctx");
+			goto out;
+		}
+
+		/* collect target */
+		cur = cpuc->cpuperf_target;
+		target_sum += cur;
+		target_min = cur < target_min ? cur : target_min;
+		target_max = cur > target_max ? cur : target_max;
+	}
+
+	cpuperf_min = cur_min;
+	cpuperf_avg = cur_sum * SCX_CPUPERF_ONE / cap_sum;
+	cpuperf_max = cur_max;
+
+	cpuperf_target_min = target_min;
+	cpuperf_target_avg = target_sum / nr_online_cpus;
+	cpuperf_target_max = target_max;
+out:
+	scx_bpf_put_cpumask(online);
+}
+
+static int monitor_timerfn(void *map, int *key, struct bpf_timer *timer)
+{
+	monitor_cpuperf();
+
+	bpf_timer_start(timer, ONE_SEC_IN_NS, 0);
+	return 0;
+}
+
 s32 BPF_STRUCT_OPS_SLEEPABLE(qmap_init)
 {
+	u32 key = 0;
+	struct bpf_timer *timer;
+	s32 ret;
+
 	print_cpus();
 
-	return scx_bpf_create_dsq(SHARED_DSQ, -1);
+	ret = scx_bpf_create_dsq(SHARED_DSQ, -1);
+	if (ret)
+		return ret;
+
+	timer = bpf_map_lookup_elem(&monitor_timer, &key);
+	if (!timer)
+		return -ESRCH;
+
+	bpf_timer_init(timer, &monitor_timer, CLOCK_MONOTONIC);
+	bpf_timer_set_callback(timer, monitor_timerfn);
+
+	return bpf_timer_start(timer, ONE_SEC_IN_NS, 0);
 }
 
 void BPF_STRUCT_OPS(qmap_exit, struct scx_exit_info *ei)
@@ -509,6 +644,7 @@  SCX_OPS_DEFINE(qmap_ops,
 	       .enqueue			= (void *)qmap_enqueue,
 	       .dequeue			= (void *)qmap_dequeue,
 	       .dispatch		= (void *)qmap_dispatch,
+	       .tick			= (void *)qmap_tick,
 	       .core_sched_before	= (void *)qmap_core_sched_before,
 	       .cpu_release		= (void *)qmap_cpu_release,
 	       .init_task		= (void *)qmap_init_task,
--- a/tools/sched_ext/scx_qmap.c
+++ b/tools/sched_ext/scx_qmap.c
@@ -116,6 +116,14 @@  int main(int argc, char **argv)
 		       nr_enqueued, nr_dispatched, nr_enqueued - nr_dispatched,
 		       skel->bss->nr_reenqueued, skel->bss->nr_dequeued,
 		       skel->bss->nr_core_sched_execed);
+		if (__COMPAT_has_ksym("scx_bpf_cpuperf_cur"))
+			printf("cpuperf: cur min/avg/max=%u/%u/%u target min/avg/max=%u/%u/%u\n",
+			       skel->bss->cpuperf_min,
+			       skel->bss->cpuperf_avg,
+			       skel->bss->cpuperf_max,
+			       skel->bss->cpuperf_target_min,
+			       skel->bss->cpuperf_target_avg,
+			       skel->bss->cpuperf_target_max);
 		fflush(stdout);
 		sleep(1);
 	}