[PATCH v5 3/3] sched/cputime: Add steal time support to full dynticks CPU time accounting

[Wanpeng Li]

From: Wanpeng Li <wanpeng...@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-by: Rik van Riel <r...@redhat.com>
Cc: Ingo Molnar <mi...@kernel.org>
Cc: Peter Zijlstra (Intel) <pet...@infradead.org>
Cc: Rik van Riel <r...@redhat.com>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Frederic Weisbecker <fweis...@gmail.com>
Cc: Paolo Bonzini <pbonz...@redhat.com>
Cc: Radim Krčmář <rkrc...@redhat.com>
Signed-off-by: Wanpeng Li <wanpeng...@hotmail.com>
---
v4 -> v5:
 * apply same logic to account_idle_time, so change get_vtime_delta instead
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 | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 75f98c5..b62f9f8 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;
 }
 
 /*
@@ -681,12 +681,17 @@ static cputime_t vtime_delta(struct task_struct *tsk)
 static cputime_t get_vtime_delta(struct task_struct *tsk)
 {
        unsigned long now = READ_ONCE(jiffies);
-       unsigned long delta = now - tsk->vtime_snap;
+       cputime_t delta_time, steal_time;
 
+       steal_time = jiffies_to_cputime(steal_account_process_tick());
+       delta_time = jiffies_to_cputime(now - tsk->vtime_snap);
        WARN_ON_ONCE(tsk->vtime_snap_whence == VTIME_INACTIVE);
        tsk->vtime_snap = now;
 
-       return jiffies_to_cputime(delta);
+       if (steal_time < delta_time)
+               delta_time -= steal_time;
+
+       return delta_time;
 }
 
 static void __vtime_account_system(struct task_struct *tsk)
-- 
1.9.1