[PATCH v4 3/3] sched/cputime: Add steal time support to full dynticks CPU time accounting

[Wanpeng Li <kernellwp@gmail.com>]

From: Wanpeng Li <wanpeng.li@hotmail.com>

This patch adds guest steal-time support to full dynticks CPU
time accounting. After the following commit:

ff9a9b4c4334 ("sched, time: Switch VIRT_CPU_ACCOUNTING_GEN to jiffy granularity")

... time sampling became jiffy based, even if it's still listened
to ring boundaries, so steal_account_process_tick() is reused
to account how many 'ticks' are stolen-time, after the last accumulation.

Suggested-and-Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
---
v3 -> v4:
 * fix grammar errors, thanks Ingo
 * cleanup fragile codes, thanks Ingo
v2 -> v3:
 * convert steal time jiffies to cputime
v1 -> v2:
 * fix divide zero bug, thanks Rik

 kernel/sched/cputime.c | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 75f98c5..9ff036b 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -257,7 +257,7 @@ void account_idle_time(cputime_t cputime)
 		cpustat[CPUTIME_IDLE] += (__force u64) cputime;
 }
 
-static __always_inline bool steal_account_process_tick(void)
+static __always_inline unsigned long steal_account_process_tick(void)
 {
 #ifdef CONFIG_PARAVIRT
 	if (static_key_false(&paravirt_steal_enabled)) {
@@ -279,7 +279,7 @@ static __always_inline bool steal_account_process_tick(void)
 		return steal_jiffies;
 	}
 #endif
-	return false;
+	return 0;
 }
 
 /*
@@ -691,9 +691,13 @@ static cputime_t get_vtime_delta(struct task_struct *tsk)
 
 static void __vtime_account_system(struct task_struct *tsk)
 {
-	cputime_t delta_cpu = get_vtime_delta(tsk);
+	cputime_t delta_time = get_vtime_delta(tsk);
+	cputime_t steal_time = jiffies_to_cputime(steal_account_process_tick());
 
-	account_system_time(tsk, irq_count(), delta_cpu, cputime_to_scaled(delta_cpu));
+	if (steal_time < delta_time) {
+		delta_time -= steal_time;
+		account_system_time(tsk, irq_count(), delta_time, cputime_to_scaled(delta_time));
+	}
 }
 
 void vtime_account_system(struct task_struct *tsk)
@@ -718,13 +722,18 @@ void vtime_gen_account_irq_exit(struct task_struct *tsk)
 
 void vtime_account_user(struct task_struct *tsk)
 {
-	cputime_t delta_cpu;
+	cputime_t delta_time, steal_time;
 
 	write_seqcount_begin(&tsk->vtime_seqcount);
 	tsk->vtime_snap_whence = VTIME_SYS;
 	if (vtime_delta(tsk)) {
-		delta_cpu = get_vtime_delta(tsk);
-		account_user_time(tsk, delta_cpu, cputime_to_scaled(delta_cpu));
+		delta_time = get_vtime_delta(tsk);
+		steal_time = jiffies_to_cputime(steal_account_process_tick());
+
+		if (steal_time < delta_time) {
+			delta_time -= steal_time;
+			account_user_time(tsk, delta_time, cputime_to_scaled(delta_time));
+		}
 	}
 	write_seqcount_end(&tsk->vtime_seqcount);
 }
-- 
1.9.1