Messages in this thread | | | Date | Tue, 6 Jun 2023 22:10:43 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH v7 19/21] timer: Implement the hierarchical pull model |
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Le Wed, May 24, 2023 at 09:06:27AM +0200, Anna-Maria Behnsen a écrit : > +u64 tmigr_cpu_deactivate(u64 nextexp) > +{ > + struct tmigr_cpu *tmc = this_cpu_ptr(&tmigr_cpu); > + u64 ret; > + > + if (!is_tmigr_enabled() || !tmc->tmgroup || !tmc->online) > + return nextexp; > + > + raw_spin_lock(&tmc->lock); > + > + /* > + * CPU is already deactivated in timer migration > + * hierarchy. tick_nohz_get_sleep_length() calls > + * tick_nohz_next_event() and thereby timer idle path is > + * executed once more. tmc->wakeup holds the first timer, when > + * timer migration hierarchy is completely idle and remote > + * expiry was done.
This can also hold the first timer in the hierarchy on nodes having no true migrator, but still with upper nodes having potentially a migrator, right??
> + * If there is no new next expiry value > + * handed in which should be inserted into the timer migration > + * hierarchy, wakeup value is returned. > + */ > + if (tmc->idle) { > + ret = tmc->wakeup; > + > + tmc->wakeup = KTIME_MAX; > + > + if (nextexp != KTIME_MAX) {
This seem to assume that tick_nohz_next_event() on the last idle CPU in an idle hierarchy is always called right after a timer interrupt arriving on time (ie: right after a call to tmigr_handle_remote()), but this can actually be called after any interrupt. Can the following happen or am I overlooking something?
do_idle() { // ===> <IRQ> tmigr_handle_remote() { // find some timer in the hierarchy // expiring in 2 jiffies tmc->wakeup = jiffies + 2 } //<=== </IRQ> tick_nohz_get_sleep_length() { get_next_timer_interrupt() { tmigr_cpu_deactivate() { wakeup = tmc->wakeup tmc->wakeup = KTIME_MAX return wakeup // jiffies + 2 } } } tick_nohz_idle_stop_tick() { // SLEEP 2 jiffies }
// ===> <IRQ> // whatever IRQ that is not timer // or a timer IRQ firing too early //<=== </IRQ> tick_nohz_get_sleep_length() { get_next_timer_interrupt() { tmigr_cpu_deactivate() { wakeup = tmc->wakeup tmc->wakeup = KTIME_MAX return wakeup // KTIME_MAX } } } tick_nohz_idle_stop_tick() { // SLEEP forever, misses the timer in 2 jiffies } }
Thanks.
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