Messages in this thread Patch in this message | | | From | "Rafael J. Wysocki" <> | Subject | [PATCH v3] cpuidle: poll_state: Add time limit to poll_idle() | Date | Wed, 14 Mar 2018 15:08:57 +0100 |
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From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
If poll_idle() is allowed to spin until need_resched() returns 'true', it may actually spin for a much longer time than expected by the idle governor, since set_tsk_need_resched() is not always called by the timer interrupt handler. If that happens, the CPU may spend much more time than anticipated in the "polling" state.
To prevent that from happening, limit the time of the spinning loop in poll_idle().
Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> ---
v2 -> v3: Use local_clock() for time measurements and drop the counter, since that should be lightweight enough (as suggested by Peter).
--- drivers/cpuidle/poll_state.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)
Index: linux-pm/drivers/cpuidle/poll_state.c =================================================================== --- linux-pm.orig/drivers/cpuidle/poll_state.c +++ linux-pm/drivers/cpuidle/poll_state.c @@ -6,15 +6,24 @@ #include <linux/cpuidle.h> #include <linux/sched.h> +#include <linux/sched/clock.h> #include <linux/sched/idle.h> +#define POLL_IDLE_TIME_LIMIT (TICK_NSEC / 16) + static int __cpuidle poll_idle(struct cpuidle_device *dev, struct cpuidle_driver *drv, int index) { + u64 time_start = local_clock(); + local_irq_enable(); if (!current_set_polling_and_test()) { - while (!need_resched()) + while (!need_resched()) { cpu_relax(); + + if (local_clock() - time_start > POLL_IDLE_TIME_LIMIT) + break; + } } current_clr_polling();
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