Messages in this thread |  | | Subject | Re: [PATCH 03/33] cputime: Generic on-demand virtual cputime accounting | From | Steven Rostedt <> | Date | Tue, 08 Jan 2013 15:45:12 -0500 |
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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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