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    SubjectRe: [PATCH 03/33] cputime: Generic on-demand virtual cputime accounting
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    On Tue, 2013-01-08 at 03:08 +0100, Frederic Weisbecker wrote:

    > +#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
    > +static DEFINE_PER_CPU(long, last_jiffies) = INITIAL_JIFFIES;
    > +
    > +static cputime_t get_vtime_delta(void)
    > +{
    > + long delta;
    > +
    > + delta = jiffies - __this_cpu_read(last_jiffies);
    > + __this_cpu_add(last_jiffies, delta);
    > +
    > + return jiffies_to_cputime(delta);
    > +}
    > +
    > +void vtime_account_system(struct task_struct *tsk)
    > +{
    > + cputime_t delta_cpu = get_vtime_delta();
    > +
    > + account_system_time(tsk, irq_count(), delta_cpu, cputime_to_scaled(delta_cpu));
    > +}
    > +
    > +void vtime_account_user(struct task_struct *tsk)
    > +{
    > + cputime_t delta_cpu = get_vtime_delta();
    > +
    > + /*
    > + * This is an unfortunate hack: if we flush user time only on
    > + * irq entry, we miss the jiffies update and the time is spuriously
    > + * accounted to system time.
    > + */
    > + if (context_tracking_in_user())
    > + account_user_time(tsk, delta_cpu, cputime_to_scaled(delta_cpu));

    Hmm, you called get_vtime_delta() up above, which updates the
    last_jiffies per_cpu variable, but if for some reason,
    context_tracking_in_user() isn't true, we throw away the delta. What
    happens to those lost jiffies? They go nowhere.

    Shouldn't it be? :

    if (context_tracking_in_user()) {
    delta_cpu = get_vtime_delta();
    account_user_time(tsk, delta_cpu, cputime_to_scaled(delta_cpu));
    }

    -- Steve

    > +}
    > +
    > +void vtime_account_idle(struct task_struct *tsk)
    > +{
    > + cputime_t delta_cpu = get_vtime_delta();
    > +
    > + account_idle_time(delta_cpu);
    > +}
    > +
    > +static int __cpuinit vtime_cpu_notify(struct notifier_block *self,
    > + unsigned long action, void *hcpu)
    > +{
    > + long cpu = (long)hcpu;
    > + long *last_jiffies_cpu = per_cpu_ptr(&last_jiffies, cpu);
    > +
    > + switch (action) {
    > + case CPU_UP_PREPARE:
    > + case CPU_UP_PREPARE_FROZEN:
    > + /*
    > + * CHECKME: ensure that's visible by the CPU
    > + * once it wakes up
    > + */
    > + *last_jiffies_cpu = jiffies;
    > + default:
    > + break;
    > + }
    > +
    > + return NOTIFY_OK;
    > +}
    > +
    > +static int __init init_vtime(void)
    > +{
    > + cpu_notifier(vtime_cpu_notify, 0);
    > + return 0;
    > +}
    > +early_initcall(init_vtime);
    > +#endif /* CONFIG_VIRT_CPU_ACCOUNTING_GEN */




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