[PATCH 2/5] nohz,cputime: remove VTIME_GEN vtime irq time code

[riel@redhat.com]

From: Rik van Riel <riel@redhat.com>

The CONFIG_VIRT_CPU_ACCOUNTING_GEN irq time tracking code does not
appear to currently work right.

On CPUs that are nohz_full, people typically do not assign IRQs.
On the housekeeping CPU (when a system is booted up with nohz_full),
sampling should work ok to determine irq and softirq time use, but
that only covers the housekeeping CPU itself, not the other
non-nohz_full CPUs.

On CPUs that are nohz_idle (the typical way a distro kernel is
booted), irq time is not accounted at all while the CPU is idle,
due to the lack of timer ticks.

Remove the VTIME_GEN vtime irq time code. The next patch will
allow NO_HZ_FULL kernels to use the IRQ_TIME_ACCOUNTING code.

Signed-off-by: Rik van Riel <riel@redhat.com>
---
 include/linux/vtime.h  | 32 +++++++++++++----------------
 kernel/sched/cputime.c | 55 ++++++++++++++++++++++++++++----------------------
 2 files changed, 45 insertions(+), 42 deletions(-)

diff --git a/include/linux/vtime.h b/include/linux/vtime.h
index fa2196990f84..3b384bf5ce1a 100644
--- a/include/linux/vtime.h
+++ b/include/linux/vtime.h
@@ -64,17 +64,6 @@ extern void vtime_account_system(struct task_struct *tsk);
 extern void vtime_account_idle(struct task_struct *tsk);
 extern void vtime_account_user(struct task_struct *tsk);
 
-#ifdef __ARCH_HAS_VTIME_ACCOUNT
-extern void vtime_account_irq_enter(struct task_struct *tsk);
-#else
-extern void vtime_common_account_irq_enter(struct task_struct *tsk);
-static inline void vtime_account_irq_enter(struct task_struct *tsk)
-{
-	if (vtime_accounting_cpu_enabled())
-		vtime_common_account_irq_enter(tsk);
-}
-#endif /* __ARCH_HAS_VTIME_ACCOUNT */
-
 #else /* !CONFIG_VIRT_CPU_ACCOUNTING */
 
 static inline void vtime_task_switch(struct task_struct *prev) { }
@@ -85,13 +74,8 @@ static inline void vtime_account_irq_enter(struct task_struct *tsk) { }
 
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
 extern void arch_vtime_task_switch(struct task_struct *tsk);
-extern void vtime_gen_account_irq_exit(struct task_struct *tsk);
-
-static inline void vtime_account_irq_exit(struct task_struct *tsk)
-{
-	if (vtime_accounting_cpu_enabled())
-		vtime_gen_account_irq_exit(tsk);
-}
+static inline void vtime_account_irq_enter(struct task_struct *tsk) { }
+static inline void vtime_account_irq_exit(struct task_struct *tsk) { }
 
 extern void vtime_user_enter(struct task_struct *tsk);
 
@@ -113,6 +97,18 @@ static inline void vtime_user_exit(struct task_struct *tsk) { }
 static inline void vtime_guest_enter(struct task_struct *tsk) { }
 static inline void vtime_guest_exit(struct task_struct *tsk) { }
 static inline void vtime_init_idle(struct task_struct *tsk, int cpu) { }
+
+#ifdef __ARCH_HAS_VTIME_ACCOUNT
+extern void vtime_account_irq_enter(struct task_struct *tsk);
+#else
+extern void vtime_common_account_irq_enter(struct task_struct *tsk);
+static inline void vtime_account_irq_enter(struct task_struct *tsk)
+{
+	if (vtime_accounting_cpu_enabled())
+		vtime_common_account_irq_enter(tsk);
+}
+#endif /* __ARCH_HAS_VTIME_ACCOUNT */
+
 #endif
 
 #ifdef CONFIG_IRQ_TIME_ACCOUNTING
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 4bd6d1b774ab..2f862dfdb520 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -103,10 +103,10 @@ static unsigned long irqtime_account_si_update(void)
 	u64 softirq;
 
 	local_irq_save(flags);
-	delta = this_cpu_read(cpu_softirq_time) - cpustat[CPUTIME_SOFTIRQ];
-	si_jiffies = cputime_to_jiffies(delta);
+	softirq = this_cpu_read(cpu_softirq_time) - cpustat[CPUTIME_SOFTIRQ];
+	si_jiffies = cputime_to_jiffies(softirq);
 	if (si_jiffies)
-		cpustat[CPUSTIME_SOFTIRQ] += jiffies_to_cputime(si_jiffies);
+		cpustat[CPUTIME_SOFTIRQ] += jiffies_to_cputime(si_jiffies);
 	local_irq_restore(flags);
 	return si_jiffies;
 }
@@ -115,6 +115,16 @@ static unsigned long irqtime_account_si_update(void)
 
 #define sched_clock_irqtime	(0)
 
+static unsigned long irqtime_account_hi_update(void)
+{
+	return 0;
+}
+
+static unsigned long irqtime_account_si_update(void)
+{
+	return 0;
+}
+
 #endif /* !CONFIG_IRQ_TIME_ACCOUNTING */
 
 static inline void task_group_account_field(struct task_struct *p, int index,
@@ -346,7 +356,6 @@ static void irqtime_account_process_tick(struct task_struct *p, int user_tick,
 {
 	cputime_t scaled = cputime_to_scaled(cputime_one_jiffy);
 	u64 cputime = (__force u64) cputime_one_jiffy;
-	u64 *cpustat = kcpustat_this_cpu->cpustat;
 	unsigned long other;
 
 	/*
@@ -703,16 +712,26 @@ static cputime_t get_vtime_delta(struct task_struct *tsk)
 	return jiffies_to_cputime(delta);
 }
 
+/* Account per-cpu irq, softirq, and steal time. Not accounted to a task. */
+static cputime_t __vtime_account_other(void)
+{
+	unsigned long ticks;
+
+	ticks = steal_account_process_tick();
+	ticks += irqtime_account_hi_update();
+	ticks += irqtime_account_si_update();
+
+	return jiffies_to_cputime(ticks);
+}
+
 static void __vtime_account_system(struct task_struct *tsk)
 {
-	cputime_t steal_time;
 	cputime_t delta_cpu = get_vtime_delta(tsk);
-	unsigned long delta_st = steal_account_process_tick();
-	steal_time = jiffies_to_cputime(delta_st);
+	cputime_t other = __vtime_account_other();
 
-	if (steal_time >= delta_cpu)
+	if (other >= delta_cpu)
 		return;
-	delta_cpu -= steal_time;
+	delta_cpu -= other;
 	account_system_time(tsk, irq_count(), delta_cpu, cputime_to_scaled(delta_cpu));
 }
 
@@ -726,16 +745,6 @@ void vtime_account_system(struct task_struct *tsk)
 	write_seqcount_end(&tsk->vtime_seqcount);
 }
 
-void vtime_gen_account_irq_exit(struct task_struct *tsk)
-{
-	write_seqcount_begin(&tsk->vtime_seqcount);
-	if (vtime_delta(tsk))
-		__vtime_account_system(tsk);
-	if (context_tracking_in_user())
-		tsk->vtime_snap_whence = VTIME_USER;
-	write_seqcount_end(&tsk->vtime_seqcount);
-}
-
 void vtime_account_user(struct task_struct *tsk)
 {
 	cputime_t delta_cpu;
@@ -743,16 +752,14 @@ void vtime_account_user(struct task_struct *tsk)
 	write_seqcount_begin(&tsk->vtime_seqcount);
 	tsk->vtime_snap_whence = VTIME_SYS;
 	if (vtime_delta(tsk)) {
-		cputime_t steal_time;
-		unsigned long delta_st = steal_account_process_tick();
+		cputime_t other = __vtime_account_other();
 		delta_cpu = get_vtime_delta(tsk);
-		steal_time = jiffies_to_cputime(delta_st);
 
-		if (steal_time >= delta_cpu) {
+		if (other >= delta_cpu) {
 			write_seqcount_end(&tsk->vtime_seqcount);
 			return;
 		}
-		delta_cpu -= steal_time;
+		delta_cpu -= other;
 		account_user_time(tsk, delta_cpu, cputime_to_scaled(delta_cpu));
 	}
 	write_seqcount_end(&tsk->vtime_seqcount);
-- 
2.5.5