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Subject[PATCH 5/7] 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>
CC: Anthony Liguori <aliguori@us.ibm.com>
CC: Eric B Munson <emunson@mgebm.net>
---
kernel/sched.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 45 insertions(+), 0 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 3f2e502..154cb14 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -75,6 +75,7 @@
#include <asm/tlb.h>
#include <asm/irq_regs.h>
#include <asm/mutex.h>
+#include <asm/paravirt.h>

#include "sched_cpupri.h"
#include "workqueue_sched.h"
@@ -528,6 +529,7 @@ struct rq {
#ifdef CONFIG_IRQ_TIME_ACCOUNTING
u64 prev_irq_time;
#endif
+ u64 prev_steal_time;

/* calc_load related fields */
unsigned long calc_load_update;
@@ -3705,6 +3707,41 @@ 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 inline int touch_steal_time(int is_idle)
+{
+ u64 steal, st = 0;
+
+ if (static_branch(&paravirt_steal_enabled)) {
+
+ steal = paravirt_steal_clock(smp_processor_id());
+
+ steal -= this_rq()->prev_steal_time;
+ this_rq()->prev_steal_time += steal;
+
+ if (is_idle || (steal < TICK_NSEC))
+ return 0;
+
+ while (steal > TICK_NSEC) {
+ steal -= TICK_NSEC;
+ st++;
+ }
+
+ account_steal_time(st);
+ return 1;
+ }
+ return 0;
+}
+
+/*
* 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
@@ -3716,6 +3753,9 @@ 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);
@@ -3802,6 +3842,9 @@ void account_system_time(struct task_struct *p, int hardirq_offset,
struct cpu_usage_stat *cpustat = &kstat_this_cpu.cpustat;
cputime64_t *target_cputime64;

+ if (touch_steal_time(0))
+ return;
+
if ((p->flags & PF_VCPU) && (irq_count() - hardirq_offset == 0)) {
account_guest_time(p, cputime, cputime_scaled);
return;
@@ -3839,6 +3882,8 @@ 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
--
1.7.3.4


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