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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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