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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