Merge branch 'idle-time-acc' into features

Heiko Carstens says:

===================
This is supposed to improve s390 idle time accounting, and brings it
back to the state it was before arch_cpu_idle_time() was removed from
s390 [3].

In result all cpu time accounting is done by the s390 architecture backend
again, instead of having a mix of architecure specific and common code
accounting (common code: idle, s390 architecture: everything else).
===================

Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

arch/s390/include/asm/idle.h

@@ -10,20 +10,18 @@
 
 #include <linux/percpu-defs.h>
 #include <linux/types.h>
-#include <linux/device.h>
+#include <asm/tod_types.h>
 
 struct s390_idle_data {
-	bool	      idle_dyntick;
-	unsigned long idle_count;
-	unsigned long idle_time;
-	unsigned long clock_idle_enter;
+#ifdef CONFIG_NO_HZ_COMMON
+	bool	      in_idle;
+#endif
 	unsigned long timer_idle_enter;
 	unsigned long mt_cycles_enter[8];
+	union tod_clock clock_idle_enter;
+	union tod_clock clock_idle_exit;
 };
 
 DECLARE_PER_CPU(struct s390_idle_data, s390_idle);
 
-extern struct device_attribute dev_attr_idle_count;
-extern struct device_attribute dev_attr_idle_time_us;
-
 #endif /* _S390_IDLE_H */

arch/s390/include/asm/lowcore.h

@@ -10,6 +10,7 @@
 #define _ASM_S390_LOWCORE_H
 
 #include <linux/types.h>
+#include <asm/tod_types.h>
 #include <asm/machine.h>
 #include <asm/ptrace.h>
 #include <asm/ctlreg.h>
@@ -125,8 +126,7 @@ struct lowcore {
 	__u64	avg_steal_timer;		/* 0x0300 */
 	__u64	last_update_timer;		/* 0x0308 */
 	__u64	last_update_clock;		/* 0x0310 */
-	__u64	int_clock;			/* 0x0318 */
-	__u8	pad_0x0320[0x0328-0x0320];	/* 0x0320 */
+	union tod_clock int_clock;		/* 0x0318 */
 	__u64	clock_comparator;		/* 0x0328 */
 	__u8	pad_0x0330[0x0340-0x0330];	/* 0x0330 */
 

arch/s390/include/asm/timex.h

@@ -12,6 +12,7 @@
 
 #include <linux/preempt.h>
 #include <linux/time64.h>
+#include <asm/tod_types.h>
 #include <asm/lowcore.h>
 #include <asm/machine.h>
 #include <asm/asm.h>
@@ -21,25 +22,6 @@
 
 extern u64 clock_comparator_max;
 
-union tod_clock {
-	__uint128_t val;
-	struct {
-		__uint128_t ei	:  8; /* epoch index */
-		__uint128_t tod : 64; /* bits 0-63 of tod clock */
-		__uint128_t	: 40;
-		__uint128_t pf	: 16; /* programmable field */
-	};
-	struct {
-		__uint128_t eitod : 72; /* epoch index + bits 0-63 tod clock */
-		__uint128_t	  : 56;
-	};
-	struct {
-		__uint128_t us	: 60; /* micro-seconds */
-		__uint128_t sus	: 12; /* sub-microseconds */
-		__uint128_t	: 56;
-	};
-} __packed;
-
 /* Inline functions for clock register access. */
 static inline int set_tod_clock(__u64 time)
 {

arch/s390/include/asm/tod_types.h

@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _ASM_S390_TOD_TYPES_H
+#define _ASM_S390_TOD_TYPES_H
+
+#include <linux/types.h>
+
+#ifndef __ASSEMBLER__
+
+union tod_clock {
+	__uint128_t val;
+	struct {
+		__uint128_t ei	:  8; /* epoch index */
+		__uint128_t tod : 64; /* bits 0-63 of tod clock */
+		__uint128_t	: 40;
+		__uint128_t pf	: 16; /* programmable field */
+	};
+	struct {
+		__uint128_t eitod : 72; /* epoch index + bits 0-63 tod clock */
+		__uint128_t	  : 56;
+	};
+	struct {
+		__uint128_t us	: 60; /* micro-seconds */
+		__uint128_t sus	: 12; /* sub-microseconds */
+		__uint128_t	: 56;
+	};
+} __packed;
+
+#endif
+#endif

arch/s390/include/asm/vtime.h

@@ -48,8 +48,8 @@ static inline void update_timer_idle(void)
 	 * The accounted CPU times will be subtracted again from steal_timer
 	 * when accumulated steal time is calculated in do_account_vtime().
 	 */
-	lc->steal_timer += idle->clock_idle_enter - lc->last_update_clock;
-	lc->last_update_clock = lc->int_clock;
+	lc->steal_timer += idle->clock_idle_enter.tod - lc->last_update_clock;
+	lc->last_update_clock = lc->int_clock.tod;
 	lc->system_timer += lc->last_update_timer - idle->timer_idle_enter;
 	lc->last_update_timer = lc->sys_enter_timer;
 }

arch/s390/kernel/asm-offsets.c

@@ -11,9 +11,11 @@
 #include <linux/purgatory.h>
 #include <linux/pgtable.h>
 #include <linux/ftrace_regs.h>
+#include <linux/kernel_stat.h>
 #include <asm/kvm_host_types.h>
 #include <asm/stacktrace.h>
 #include <asm/ptrace.h>
+#include <asm/idle.h>
 
 int main(void)
 {
@@ -128,6 +130,7 @@ int main(void)
 	OFFSET(__LC_LAST_UPDATE_CLOCK, lowcore, last_update_clock);
 	OFFSET(__LC_INT_CLOCK, lowcore, int_clock);
 	OFFSET(__LC_CURRENT, lowcore, current_task);
+	OFFSET(__LC_PERCPU_OFFSET, lowcore, percpu_offset);
 	OFFSET(__LC_KERNEL_STACK, lowcore, kernel_stack);
 	OFFSET(__LC_ASYNC_STACK, lowcore, async_stack);
 	OFFSET(__LC_NODAT_STACK, lowcore, nodat_stack);
@@ -180,6 +183,10 @@ int main(void)
 	DEFINE(OLDMEM_SIZE, PARMAREA + offsetof(struct parmarea, oldmem_size));
 	DEFINE(COMMAND_LINE, PARMAREA + offsetof(struct parmarea, command_line));
 	DEFINE(MAX_COMMAND_LINE_SIZE, PARMAREA + offsetof(struct parmarea, max_command_line_size));
+	OFFSET(__IDLE_CLOCK_EXIT, s390_idle_data, clock_idle_exit);
+#ifdef CONFIG_NO_HZ_COMMON
+	OFFSET(__KCPUSTAT_SEQUENCE, kernel_cpustat, idle_sleeptime_seq);
+#endif
 	OFFSET(__FTRACE_REGS_PT_REGS, __arch_ftrace_regs, regs);
 	DEFINE(__FTRACE_REGS_SIZE, sizeof(struct __arch_ftrace_regs));
 

arch/s390/kernel/entry.S

@@ -379,8 +379,19 @@ SYM_CODE_END(pgm_check_handler)
 SYM_CODE_START(\name)
 	STMG_LC	%r8,%r15,__LC_SAVE_AREA
 	GET_LC	%r13
-	stckf	__LC_INT_CLOCK(%r13)
+#ifdef CONFIG_NO_HZ_COMMON
+	larl	%r12,kernel_cpustat
+	ag	%r12,__LC_PERCPU_OFFSET(%r13)
+	asi	__KCPUSTAT_SEQUENCE(%r12),1
+#endif
+	stcke	__LC_INT_CLOCK(%r13)
 	stpt	__LC_SYS_ENTER_TIMER(%r13)
+	larl	%r10,s390_idle
+	ag	%r10,__LC_PERCPU_OFFSET(%r13)
+	mvc	__IDLE_CLOCK_EXIT(16,%r10),__LC_INT_CLOCK(%r13)
+#ifdef CONFIG_NO_HZ_COMMON
+	asi	__KCPUSTAT_SEQUENCE(%r12),1
+#endif
 	STBEAR	__LC_LAST_BREAK(%r13)
 	BPOFF
 	lmg	%r8,%r9,\lc_old_psw(%r13)
@@ -407,7 +418,6 @@ SYM_CODE_START(\name)
 	xgr	%r5,%r5
 	xgr	%r6,%r6
 	xgr	%r7,%r7
-	xgr	%r10,%r10
 	xgr	%r12,%r12
 	xc	__PT_FLAGS(8,%r11),__PT_FLAGS(%r11)
 	mvc	__PT_R8(64,%r11),__LC_SAVE_AREA(%r13)

arch/s390/kernel/idle.c

@@ -9,6 +9,7 @@
 
 #include <linux/kernel.h>
 #include <linux/kernel_stat.h>
+#include <linux/sched/stat.h>
 #include <linux/notifier.h>
 #include <linux/init.h>
 #include <linux/cpu.h>
@@ -21,22 +22,109 @@
 
 DEFINE_PER_CPU(struct s390_idle_data, s390_idle);
 
-void account_idle_time_irq(void)
+static __always_inline void __account_idle_time_irq(void)
 {
 	struct s390_idle_data *idle = this_cpu_ptr(&s390_idle);
 	unsigned long idle_time;
 
-	idle_time = get_lowcore()->int_clock - idle->clock_idle_enter;
-
-	/* Account time spent with enabled wait psw loaded as idle time. */
-	__atomic64_add(idle_time, &idle->idle_time);
-	__atomic64_add_const(1, &idle->idle_count);
-
-	/* Dyntick idle time accounted by nohz/scheduler */
-	if (!idle->idle_dyntick)
-		account_idle_time(cputime_to_nsecs(idle_time));
+	idle_time = idle->clock_idle_exit.tod - idle->clock_idle_enter.tod;
+	account_idle_time(cputime_to_nsecs(idle_time));
 }
 
+static __always_inline void __account_idle_time_setup(void)
+{
+	struct s390_idle_data *idle = this_cpu_ptr(&s390_idle);
+
+	store_tod_clock_ext(&idle->clock_idle_enter);
+	idle->timer_idle_enter = get_cpu_timer();
+	idle->clock_idle_exit = idle->clock_idle_enter;
+}
+
+#ifdef CONFIG_NO_HZ_COMMON
+
+static u64 arch_cpu_in_idle_time(int cpu)
+{
+	struct s390_idle_data *idle = &per_cpu(s390_idle, cpu);
+	union tod_clock now;
+	u64 idle_time;
+
+	if (!idle->in_idle)
+		return 0;
+	store_tod_clock_ext(&now);
+	if (tod_after(idle->clock_idle_exit.tod, idle->clock_idle_enter.tod))
+		idle_time = idle->clock_idle_exit.tod - idle->clock_idle_enter.tod;
+	else
+		idle_time = now.tod - idle->clock_idle_enter.tod;
+	return cputime_to_nsecs(idle_time);
+}
+
+static u64 arch_cpu_idle_time(int cpu, enum cpu_usage_stat idx, bool compute_delta)
+{
+	struct kernel_cpustat *kc = &kcpustat_cpu(cpu);
+	u64 *cpustat = kc->cpustat;
+	unsigned int seq;
+	u64 idle_time;
+
+	/*
+	 * The open coded seqcount writer in entry.S relies on the
+	 * raw counting mechanism without any writer protection.
+	 */
+	typecheck(typeof(kc->idle_sleeptime_seq), seqcount_t);
+	do {
+		seq = read_seqcount_begin(&kc->idle_sleeptime_seq);
+		idle_time = cpustat[idx];
+		if (compute_delta)
+			idle_time += arch_cpu_in_idle_time(cpu);
+	} while (read_seqcount_retry(&kc->idle_sleeptime_seq, seq));
+	return idle_time;
+}
+
+u64 arch_kcpustat_field_idle(int cpu)
+{
+	return arch_cpu_idle_time(cpu, CPUTIME_IDLE, !nr_iowait_cpu(cpu));
+}
+
+u64 arch_kcpustat_field_iowait(int cpu)
+{
+	return arch_cpu_idle_time(cpu, CPUTIME_IOWAIT, nr_iowait_cpu(cpu));
+}
+
+void account_idle_time_irq(void)
+{
+	struct s390_idle_data *idle = this_cpu_ptr(&s390_idle);
+	struct kernel_cpustat *kc = kcpustat_this_cpu;
+
+	write_seqcount_begin(&kc->idle_sleeptime_seq);
+	idle->in_idle = false;
+	__account_idle_time_irq();
+	write_seqcount_end(&kc->idle_sleeptime_seq);
+}
+
+static __always_inline void account_idle_time_setup(void)
+{
+	struct s390_idle_data *idle = this_cpu_ptr(&s390_idle);
+	struct kernel_cpustat *kc = kcpustat_this_cpu;
+
+	raw_write_seqcount_begin(&kc->idle_sleeptime_seq);
+	idle->in_idle = true;
+	__account_idle_time_setup();
+	raw_write_seqcount_end(&kc->idle_sleeptime_seq);
+}
+
+#else  /* CONFIG_NO_HZ_COMMON */
+
+void account_idle_time_irq(void)
+{
+	__account_idle_time_irq();
+}
+
+static __always_inline void account_idle_time_setup(void)
+{
+	__account_idle_time_setup();
+}
+
+#endif /* CONFIG_NO_HZ_COMMON */
+
 void noinstr arch_cpu_idle(void)
 {
 	struct s390_idle_data *idle = this_cpu_ptr(&s390_idle);
@@ -49,30 +137,11 @@ void noinstr arch_cpu_idle(void)
 	set_cpu_flag(CIF_ENABLED_WAIT);
 	if (smp_cpu_mtid)
 		stcctm(MT_DIAG, smp_cpu_mtid, (u64 *)&idle->mt_cycles_enter);
-	idle->clock_idle_enter = get_tod_clock_fast();
-	idle->timer_idle_enter = get_cpu_timer();
+	account_idle_time_setup();
 	bpon();
 	__load_psw_mask(psw_mask);
 }
 
-static ssize_t show_idle_count(struct device *dev,
-			       struct device_attribute *attr, char *buf)
-{
-	struct s390_idle_data *idle = &per_cpu(s390_idle, dev->id);
-
-	return sysfs_emit(buf, "%lu\n", READ_ONCE(idle->idle_count));
-}
-DEVICE_ATTR(idle_count, 0444, show_idle_count, NULL);
-
-static ssize_t show_idle_time(struct device *dev,
-			      struct device_attribute *attr, char *buf)
-{
-	struct s390_idle_data *idle = &per_cpu(s390_idle, dev->id);
-
-	return sysfs_emit(buf, "%lu\n", READ_ONCE(idle->idle_time) >> 12);
-}
-DEVICE_ATTR(idle_time_us, 0444, show_idle_time, NULL);
-
 void arch_cpu_idle_enter(void)
 {
 }

arch/s390/kernel/irq.c

@@ -104,9 +104,10 @@ static const struct irq_class irqclass_sub_desc[] = {
 
 static void do_IRQ(struct pt_regs *regs, int irq)
 {
-	if (tod_after_eq(get_lowcore()->int_clock,
-			 get_lowcore()->clock_comparator))
-		/* Serve timer interrupts first. */
+	struct lowcore *lc = get_lowcore();
+
+	/* Serve timer interrupts first */
+	if (tod_after_eq(lc->int_clock.tod, lc->clock_comparator))
 		clock_comparator_work();
 	generic_handle_irq(irq);
 }

arch/s390/kernel/smp.c

@@ -54,7 +54,6 @@
 #include <asm/debug.h>
 #include <asm/os_info.h>
 #include <asm/sigp.h>
-#include <asm/idle.h>
 #include <asm/nmi.h>
 #include <asm/stacktrace.h>
 #include <asm/topology.h>
@@ -1085,31 +1084,6 @@ static struct attribute_group cpu_common_attr_group = {
 	.attrs = cpu_common_attrs,
 };
 
-static struct attribute *cpu_online_attrs[] = {
-	&dev_attr_idle_count.attr,
-	&dev_attr_idle_time_us.attr,
-	NULL,
-};
-
-static struct attribute_group cpu_online_attr_group = {
-	.attrs = cpu_online_attrs,
-};
-
-static int smp_cpu_online(unsigned int cpu)
-{
-	struct cpu *c = per_cpu_ptr(&cpu_devices, cpu);
-
-	return sysfs_create_group(&c->dev.kobj, &cpu_online_attr_group);
-}
-
-static int smp_cpu_pre_down(unsigned int cpu)
-{
-	struct cpu *c = per_cpu_ptr(&cpu_devices, cpu);
-
-	sysfs_remove_group(&c->dev.kobj, &cpu_online_attr_group);
-	return 0;
-}
-
 bool arch_cpu_is_hotpluggable(int cpu)
 {
 	return !!cpu;
@@ -1175,18 +1149,13 @@ static DEVICE_ATTR_WO(rescan);
 static int __init s390_smp_init(void)
 {
 	struct device *dev_root;
-	int rc;
+	int rc = 0;
 
 	dev_root = bus_get_dev_root(&cpu_subsys);
 	if (dev_root) {
 		rc = device_create_file(dev_root, &dev_attr_rescan);
 		put_device(dev_root);
-		if (rc)
-			return rc;
 	}
-	rc = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "s390/smp:online",
-			       smp_cpu_online, smp_cpu_pre_down);
-	rc = rc <= 0 ? rc : 0;
 	return rc;
 }
 subsys_initcall(s390_smp_init);

arch/s390/kernel/vtime.c

@@ -140,8 +140,6 @@ static int do_account_vtime(struct task_struct *tsk)
 
 	if (hardirq_count())
 		lc->hardirq_timer += timer;
-	else if (in_serving_softirq())
-		lc->softirq_timer += timer;
 	else
 		lc->system_timer += timer;
 
@@ -241,63 +239,14 @@ EXPORT_SYMBOL_GPL(vtime_account_kernel);
 
 void vtime_account_softirq(struct task_struct *tsk)
 {
-	if (!__this_cpu_read(s390_idle.idle_dyntick))
-		get_lowcore()->softirq_timer += vtime_delta();
-	else
-		vtime_flush(tsk);
+	get_lowcore()->softirq_timer += vtime_delta();
 }
 
 void vtime_account_hardirq(struct task_struct *tsk)
 {
-	if (!__this_cpu_read(s390_idle.idle_dyntick)) {
-		get_lowcore()->hardirq_timer += vtime_delta();
-	} else {
-		/*
-		 * In dynticks mode, the idle cputime is accounted by the nohz
-		 * subsystem. Therefore the s390 timer/clocks are reset on IRQ
-		 * entry and steal time must be accounted now.
-		 */
-		vtime_flush(tsk);
-	}
+	get_lowcore()->hardirq_timer += vtime_delta();
 }
 
-#ifdef CONFIG_NO_HZ_COMMON
-/**
- * vtime_reset - Fast forward vtime entry clocks
- *
- * Called from dynticks idle IRQ entry to fast-forward the clocks to current time
- * so that the IRQ time is still accounted by vtime while nohz cputime is paused.
- */
-void vtime_reset(void)
-{
-	vtime_reset_last_update(get_lowcore());
-}
-
-/**
- * vtime_dyntick_start - Inform vtime about entry to idle-dynticks
- *
- * Called when idle enters in dyntick mode. The idle cputime that elapsed so far
- * is flushed and the tick subsystem takes over the idle cputime accounting.
- */
-void vtime_dyntick_start(void)
-{
-	__this_cpu_write(s390_idle.idle_dyntick, true);
-	vtime_flush(current);
-}
-
-/**
- * vtime_dyntick_stop - Inform vtime about exit from idle-dynticks
- *
- * Called when idle exits from dyntick mode. The vtime entry clocks are
- * fast-forward to current time and idle accounting resumes.
- */
-void vtime_dyntick_stop(void)
-{
-	vtime_reset_last_update(get_lowcore());
-	__this_cpu_write(s390_idle.idle_dyntick, false);
-}
-#endif /* CONFIG_NO_HZ_COMMON */
-
 /*
  * Sorted add to a list. List is linear searched until first bigger
  * element is found.

drivers/s390/cio/qdio_main.c

@@ -695,7 +695,7 @@ static void qdio_int_handler_pci(struct qdio_irq *irq_ptr)
 		return;
 
 	qdio_deliver_irq(irq_ptr);
-	irq_ptr->last_data_irq_time = get_lowcore()->int_clock;
+	irq_ptr->last_data_irq_time = get_lowcore()->int_clock.tod;
 }
 
 static void qdio_handle_activate_check(struct qdio_irq *irq_ptr,

drivers/s390/cio/qdio_thinint.c

@@ -99,7 +99,7 @@ static inline u32 clear_shared_ind(void)
 static void tiqdio_thinint_handler(struct airq_struct *airq,
 				   struct tpi_info *tpi_info)
 {
-	u64 irq_time = get_lowcore()->int_clock;
+	u64 irq_time = get_lowcore()->int_clock.tod;
 	u32 si_used = clear_shared_ind();
 	struct qdio_irq *irq;
 

include/linux/kernel_stat.h

@@ -107,6 +107,30 @@ static inline unsigned long kstat_cpu_irqs_sum(unsigned int cpu)
 }
 
 #ifdef CONFIG_NO_HZ_COMMON
+
+#ifdef CONFIG_HAVE_VIRT_CPU_ACCOUNTING_IDLE
+
+static inline void kcpustat_dyntick_start(u64 now) { }
+static inline void kcpustat_dyntick_stop(u64 now) { }
+static inline void kcpustat_irq_enter(u64 now) { }
+static inline void kcpustat_irq_exit(u64 now) { }
+static inline bool kcpustat_idle_dyntick(void) { return false; }
+
+extern u64 arch_kcpustat_field_idle(int cpu);
+extern u64 arch_kcpustat_field_iowait(int cpu);
+
+static inline u64 kcpustat_field_idle(int cpu)
+{
+	return arch_kcpustat_field_idle(cpu);
+}
+
+static inline u64 kcpustat_field_iowait(int cpu)
+{
+	return arch_kcpustat_field_iowait(cpu);
+}
+
+#else /* !CONFIG_HAVE_VIRT_CPU_ACCOUNTING_IDLE */
+
 extern void kcpustat_dyntick_start(u64 now);
 extern void kcpustat_dyntick_stop(u64 now);
 extern void kcpustat_irq_enter(u64 now);
@@ -118,6 +142,9 @@ static inline bool kcpustat_idle_dyntick(void)
 {
 	return __this_cpu_read(kernel_cpustat.idle_dyntick);
 }
+
+#endif /* !CONFIG_HAVE_VIRT_CPU_ACCOUNTING_IDLE */
+
 #else
 static inline u64 kcpustat_field_idle(int cpu)
 {

include/linux/vtime.h

@@ -42,9 +42,15 @@ extern void vtime_account_irq(struct task_struct *tsk, unsigned int offset);
 extern void vtime_account_softirq(struct task_struct *tsk);
 extern void vtime_account_hardirq(struct task_struct *tsk);
 extern void vtime_flush(struct task_struct *tsk);
+#ifdef CONFIG_HAVE_VIRT_CPU_ACCOUNTING_IDLE
+static inline void vtime_reset(void) { }
+static inline void vtime_dyntick_start(void) { }
+static inline void vtime_dyntick_stop(void) { }
+#else
 extern void vtime_reset(void);
 extern void vtime_dyntick_start(void);
 extern void vtime_dyntick_stop(void);
+#endif
 #else /* !CONFIG_VIRT_CPU_ACCOUNTING_NATIVE */
 static inline void vtime_account_irq(struct task_struct *tsk, unsigned int offset) { }
 static inline void vtime_account_softirq(struct task_struct *tsk) { }

kernel/sched/cputime.c

@@ -421,7 +421,7 @@ static inline void irqtime_account_process_tick(struct task_struct *p, int user_
 						int nr_ticks) { }
 #endif /* !CONFIG_IRQ_TIME_ACCOUNTING */
 
-#ifdef CONFIG_NO_HZ_COMMON
+#if defined(CONFIG_NO_HZ_COMMON) && !defined(CONFIG_HAVE_VIRT_CPU_ACCOUNTING_IDLE)
 static void kcpustat_idle_stop(struct kernel_cpustat *kc, u64 now)
 {
 	u64 *cpustat = kc->cpustat;
@@ -560,7 +560,7 @@ static u64 kcpustat_field_dyntick(int cpu, enum cpu_usage_stat idx,
 {
 	return kcpustat_cpu(cpu).cpustat[idx];
 }
-#endif /* CONFIG_NO_HZ_COMMON */
+#endif /* CONFIG_NO_HZ_COMMON && !CONFIG_HAVE_VIRT_CPU_ACCOUNTING_IDLE */
 
 static u64 get_cpu_sleep_time_us(int cpu, enum cpu_usage_stat idx,
 				 bool compute_delta, u64 *last_update_time)