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Subject[PATCH v3 3/6] KVM-GST: KVM Steal time accounting
Date
This patch accounts steal time time in kernel/sched.
I kept it from last proposal, because I still see advantages
in it: Doing it here will give us easier access from scheduler
variables such as the cpu rq. The next patch shows an example of
usage for it.

Since functions like account_idle_time() can be called from
multiple places, not only account_process_tick(), steal time
grabbing is repeated in each account function separatedely.

Signed-off-by: Glauber Costa <glommer@redhat.com>
CC: Rik van Riel <riel@redhat.com>
CC: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Avi Kivity <avi@redhat.com>
---
include/linux/sched.h | 1 +
kernel/sched.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 48 insertions(+), 0 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index d747f94..5dbf509 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -302,6 +302,7 @@ long io_schedule_timeout(long timeout);
extern void cpu_init (void);
extern void trap_init(void);
extern void update_process_times(int user);
+extern u64 (*hypervisor_steal_time)(int cpu);
extern void scheduler_tick(void);

extern void sched_show_task(struct task_struct *p);
diff --git a/kernel/sched.c b/kernel/sched.c
index 18d38e4..60b0cf8 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -524,6 +524,8 @@ struct rq {
u64 prev_irq_time;
#endif

+ u64 prev_steal_ticks;
+
/* calc_load related fields */
unsigned long calc_load_update;
long calc_load_active;
@@ -1780,6 +1782,16 @@ static void deactivate_task(struct rq *rq, struct task_struct *p, int flags)
dec_nr_running(rq);
}

+u64 (*hypervisor_steal_time)(int cpu) = NULL;
+
+static u64 steal_time_clock(int cpu)
+{
+ if (!hypervisor_steal_time)
+ return 0;
+
+ return hypervisor_steal_time(cpu);
+}
+
#ifdef CONFIG_IRQ_TIME_ACCOUNTING

/*
@@ -3509,6 +3521,33 @@ unsigned long long thread_group_sched_runtime(struct task_struct *p)
}

/*
+ * We have to at flush steal time information every time something else
+ * is accounted. Since the accounting functions are all visible to the rest
+ * of the kernel, it gets tricky to do them in one place. This helper function
+ * helps us.
+ *
+ * When the system is idle, the concept of steal time does not apply. We just
+ * tell the underlying hypervisor that we grabbed the data, but skip steal time
+ * accounting
+ */
+static int touch_steal_time(int is_idle)
+{
+ u64 steal, st;
+
+ steal = steal_time_clock(smp_processor_id());
+
+ st = steal / TICK_NSEC - this_rq()->prev_steal_ticks;
+
+ this_rq()->prev_steal_ticks += st;
+
+ if (!st || is_idle)
+ return 0;
+
+ account_steal_time(st);
+ return 1;
+}
+
+/*
* Account user cpu time to a process.
* @p: the process that the cpu time gets accounted to
* @cputime: the cpu time spent in user space since the last update
@@ -3520,6 +3559,9 @@ void account_user_time(struct task_struct *p, cputime_t cputime,
struct cpu_usage_stat *cpustat = &kstat_this_cpu.cpustat;
cputime64_t tmp;

+ if (touch_steal_time(0))
+ return;
+
/* Add user time to process. */
p->utime = cputime_add(p->utime, cputime);
p->utimescaled = cputime_add(p->utimescaled, cputime_scaled);
@@ -3580,6 +3622,9 @@ void account_system_time(struct task_struct *p, int hardirq_offset,
struct cpu_usage_stat *cpustat = &kstat_this_cpu.cpustat;
cputime64_t tmp;

+ if (touch_steal_time(0))
+ return;
+
if ((p->flags & PF_VCPU) && (irq_count() - hardirq_offset == 0)) {
account_guest_time(p, cputime, cputime_scaled);
return;
@@ -3627,6 +3672,8 @@ void account_idle_time(cputime_t cputime)
cputime64_t cputime64 = cputime_to_cputime64(cputime);
struct rq *rq = this_rq();

+ touch_steal_time(1);
+
if (atomic_read(&rq->nr_iowait) > 0)
cpustat->iowait = cputime64_add(cpustat->iowait, cputime64);
else
--
1.7.2.3


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