[PATCH 02/14] sched/cputime: Add vtime idle task state

[Frederic Weisbecker]

Record idle as a VTIME state instead of guessing it from VTIME_SYS and
is_idle_task(). This is going to simplify the cputime read side
especially as its state machine is going to further expand in order to
fully support kcpustat on nohz_full.

Signed-off-by: Frederic Weisbecker <frede...@kernel.org>
Cc: Yauheni Kaliuta <yauheni.kali...@redhat.com>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Rik van Riel <r...@surriel.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Wanpeng Li <wanpen...@tencent.com>
Cc: Ingo Molnar <mi...@kernel.org>
---
 include/linux/sched.h  |  6 ++++--
 kernel/sched/cputime.c | 13 ++++++++-----
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index d5d07335a97b..4ae19be2c126 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -249,10 +249,12 @@ struct prev_cputime {
 enum vtime_state {
        /* Task is sleeping or running in a CPU with VTIME inactive: */
        VTIME_INACTIVE = 0,
-       /* Task runs in userspace in a CPU with VTIME active: */
-       VTIME_USER,
+       /* Task is idle */
+       VTIME_IDLE,
        /* Task runs in kernelspace in a CPU with VTIME active: */
        VTIME_SYS,
+       /* Task runs in userspace in a CPU with VTIME active: */
+       VTIME_USER,
 };
 
 struct vtime {
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 40f581692254..2e885e870aa1 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -813,7 +813,7 @@ void vtime_task_switch_generic(struct task_struct *prev)
        struct vtime *vtime = &prev->vtime;
 
        write_seqcount_begin(&vtime->seqcount);
-       if (is_idle_task(prev))
+       if (vtime->state == VTIME_IDLE)
                vtime_account_idle(prev);
        else
                __vtime_account_kernel(prev, vtime);
@@ -824,7 +824,10 @@ void vtime_task_switch_generic(struct task_struct *prev)
        vtime = &current->vtime;
 
        write_seqcount_begin(&vtime->seqcount);
-       vtime->state = VTIME_SYS;
+       if (is_idle_task(current))
+               vtime->state = VTIME_IDLE;
+       else
+               vtime->state = VTIME_SYS;
        vtime->starttime = sched_clock();
        vtime->cpu = smp_processor_id();
        write_seqcount_end(&vtime->seqcount);
@@ -837,7 +840,7 @@ void vtime_init_idle(struct task_struct *t, int cpu)
 
        local_irq_save(flags);
        write_seqcount_begin(&vtime->seqcount);
-       vtime->state = VTIME_SYS;
+       vtime->state = VTIME_IDLE;
        vtime->starttime = sched_clock();
        vtime->cpu = cpu;
        write_seqcount_end(&vtime->seqcount);
@@ -888,8 +891,8 @@ void task_cputime(struct task_struct *t, u64 *utime, u64 
*stime)
                *utime = t->utime;
                *stime = t->stime;
 
-               /* Task is sleeping, nothing to add */
-               if (vtime->state == VTIME_INACTIVE || is_idle_task(t))
+               /* Task is sleeping or idle, nothing to add */
+               if (vtime->state < VTIME_SYS)
                        continue;
 
                delta = vtime_delta(vtime);
-- 
2.23.0