sched/core: add forced idle accounting for cgroups

4feee7d previously added per-task forced idle accounting. This patch
extends this to also include cgroups.

rstat is used for cgroup accounting, except for the root, which uses
kcpustat in order to bypass the need for doing an rstat flush when
reading root stats.

Only cgroup v2 is supported. Similar to the task accounting, the cgroup
accounting requires that schedstats is enabled.

Signed-off-by: Josh Don <joshdon@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lkml.kernel.org/r/20220629211426.3329954-1-joshdon@google.com

include/linux/cgroup-defs.h

@@ -287,6 +287,10 @@ struct css_set {
 
 struct cgroup_base_stat {
 	struct task_cputime cputime;
+
+#ifdef CONFIG_SCHED_CORE
+	u64 forceidle_sum;
+#endif
 };
 
 /*

include/linux/kernel_stat.h

@@ -28,6 +28,9 @@ enum cpu_usage_stat {
 	CPUTIME_STEAL,
 	CPUTIME_GUEST,
 	CPUTIME_GUEST_NICE,
+#ifdef CONFIG_SCHED_CORE
+	CPUTIME_FORCEIDLE,
+#endif
 	NR_STATS,
 };
 
@@ -115,4 +118,8 @@ extern void account_process_tick(struct task_struct *, int user);
 
 extern void account_idle_ticks(unsigned long ticks);
 
+#ifdef CONFIG_SCHED_CORE
+extern void __account_forceidle_time(struct task_struct *tsk, u64 delta);
+#endif
+
 #endif /* _LINUX_KERNEL_STAT_H */

kernel/cgroup/rstat.c

@@ -310,6 +310,9 @@ static void cgroup_base_stat_add(struct cgroup_base_stat *dst_bstat,
 	dst_bstat->cputime.utime += src_bstat->cputime.utime;
 	dst_bstat->cputime.stime += src_bstat->cputime.stime;
 	dst_bstat->cputime.sum_exec_runtime += src_bstat->cputime.sum_exec_runtime;
+#ifdef CONFIG_SCHED_CORE
+	dst_bstat->forceidle_sum += src_bstat->forceidle_sum;
+#endif
 }
 
 static void cgroup_base_stat_sub(struct cgroup_base_stat *dst_bstat,
@@ -318,6 +321,9 @@ static void cgroup_base_stat_sub(struct cgroup_base_stat *dst_bstat,
 	dst_bstat->cputime.utime -= src_bstat->cputime.utime;
 	dst_bstat->cputime.stime -= src_bstat->cputime.stime;
 	dst_bstat->cputime.sum_exec_runtime -= src_bstat->cputime.sum_exec_runtime;
+#ifdef CONFIG_SCHED_CORE
+	dst_bstat->forceidle_sum -= src_bstat->forceidle_sum;
+#endif
 }
 
 static void cgroup_base_stat_flush(struct cgroup *cgrp, int cpu)
@@ -398,6 +404,11 @@ void __cgroup_account_cputime_field(struct cgroup *cgrp,
 	case CPUTIME_SOFTIRQ:
 		rstatc->bstat.cputime.stime += delta_exec;
 		break;
+#ifdef CONFIG_SCHED_CORE
+	case CPUTIME_FORCEIDLE:
+		rstatc->bstat.forceidle_sum += delta_exec;
+		break;
+#endif
 	default:
 		break;
 	}
@@ -411,8 +422,9 @@ void __cgroup_account_cputime_field(struct cgroup *cgrp,
  * with how it is done by __cgroup_account_cputime_field for each bit of
  * cpu time attributed to a cgroup.
  */
-static void root_cgroup_cputime(struct task_cputime *cputime)
+static void root_cgroup_cputime(struct cgroup_base_stat *bstat)
 {
+	struct task_cputime *cputime = &bstat->cputime;
 	int i;
 
 	cputime->stime = 0;
@@ -438,34 +450,54 @@ static void root_cgroup_cputime(struct task_cputime *cputime)
 		cputime->sum_exec_runtime += user;
 		cputime->sum_exec_runtime += sys;
 		cputime->sum_exec_runtime += cpustat[CPUTIME_STEAL];
+
+#ifdef CONFIG_SCHED_CORE
+		bstat->forceidle_sum += cpustat[CPUTIME_FORCEIDLE];
+#endif
 	}
 }
 
 void cgroup_base_stat_cputime_show(struct seq_file *seq)
 {
 	struct cgroup *cgrp = seq_css(seq)->cgroup;
 	u64 usage, utime, stime;
-	struct task_cputime cputime;
+	struct cgroup_base_stat bstat;
+#ifdef CONFIG_SCHED_CORE
+	u64 forceidle_time;
+#endif
 
 	if (cgroup_parent(cgrp)) {
 		cgroup_rstat_flush_hold(cgrp);
 		usage = cgrp->bstat.cputime.sum_exec_runtime;
 		cputime_adjust(&cgrp->bstat.cputime, &cgrp->prev_cputime,
 			       &utime, &stime);
+#ifdef CONFIG_SCHED_CORE
+		forceidle_time = cgrp->bstat.forceidle_sum;
+#endif
 		cgroup_rstat_flush_release();
 	} else {
-		root_cgroup_cputime(&cputime);
-		usage = cputime.sum_exec_runtime;
-		utime = cputime.utime;
-		stime = cputime.stime;
+		root_cgroup_cputime(&bstat);
+		usage = bstat.cputime.sum_exec_runtime;
+		utime = bstat.cputime.utime;
+		stime = bstat.cputime.stime;
+#ifdef CONFIG_SCHED_CORE
+		forceidle_time = bstat.forceidle_sum;
+#endif
 	}
 
 	do_div(usage, NSEC_PER_USEC);
 	do_div(utime, NSEC_PER_USEC);
 	do_div(stime, NSEC_PER_USEC);
+#ifdef CONFIG_SCHED_CORE
+	do_div(forceidle_time, NSEC_PER_USEC);
+#endif
 
 	seq_printf(seq, "usage_usec %llu\n"
 		   "user_usec %llu\n"
 		   "system_usec %llu\n",
 		   usage, utime, stime);
+
+#ifdef CONFIG_SCHED_CORE
+	seq_printf(seq, "core_sched.force_idle_usec %llu\n", forceidle_time);
+#endif
 }

kernel/sched/core_sched.c

@@ -277,7 +277,11 @@ void __sched_core_account_forceidle(struct rq *rq)
 		if (p == rq_i->idle)
 			continue;
 
-		__schedstat_add(p->stats.core_forceidle_sum, delta);
+		/*
+		 * Note: this will account forceidle to the current cpu, even
+		 * if it comes from our SMT sibling.
+		 */
+		__account_forceidle_time(p, delta);
 	}
 }
 

kernel/sched/cputime.c

@@ -226,6 +226,21 @@ void account_idle_time(u64 cputime)
 		cpustat[CPUTIME_IDLE] += cputime;
 }
 
+
+#ifdef CONFIG_SCHED_CORE
+/*
+ * Account for forceidle time due to core scheduling.
+ *
+ * REQUIRES: schedstat is enabled.
+ */
+void __account_forceidle_time(struct task_struct *p, u64 delta)
+{
+	__schedstat_add(p->stats.core_forceidle_sum, delta);
+
+	task_group_account_field(p, CPUTIME_FORCEIDLE, delta);
+}
+#endif
+
 /*
  * When a guest is interrupted for a longer amount of time, missed clock
  * ticks are not redelivered later. Due to that, this function may on