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authorRafael J. Wysocki <rafael.j.wysocki@intel.com>2018-04-04 00:17:11 +0300
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2018-04-09 12:54:07 +0300
commit554c8aa8ecade210d58a252173bb8f2106552a44 (patch)
tree6712ac8a8c4ccf95730c1c1c4cdafe595280a578 /include/linux/tick.h
parenta59855cd8c613ba4bb95147f6176360d95f75e60 (diff)
downloadlinux-554c8aa8ecade210d58a252173bb8f2106552a44.tar.xz
sched: idle: Select idle state before stopping the tick
In order to address the issue with short idle duration predictions by the idle governor after the scheduler tick has been stopped, reorder the code in cpuidle_idle_call() so that the governor idle state selection runs before tick_nohz_idle_go_idle() and use the "nohz" hint returned by cpuidle_select() to decide whether or not to stop the tick. This isn't straightforward, because menu_select() invokes tick_nohz_get_sleep_length() to get the time to the next timer event and the number returned by the latter comes from __tick_nohz_idle_stop_tick(). Fortunately, however, it is possible to compute that number without actually stopping the tick and with the help of the existing code. Namely, tick_nohz_get_sleep_length() can be made call tick_nohz_next_event(), introduced earlier, to get the time to the next non-highres timer event. If that happens, tick_nohz_next_event() need not be called by __tick_nohz_idle_stop_tick() again. If it turns out that the scheduler tick cannot be stopped going forward or the next timer event is too close for the tick to be stopped, tick_nohz_get_sleep_length() can simply return the time to the next event currently programmed into the corresponding clock event device. In addition to knowing the return value of tick_nohz_next_event(), however, tick_nohz_get_sleep_length() needs to know the time to the next highres timer event, but with the scheduler tick timer excluded, which can be computed with the help of hrtimer_get_next_event(). That minimum of that number and the tick_nohz_next_event() return value is the total time to the next timer event with the assumption that the tick will be stopped. It can be returned to the idle governor which can use it for predicting idle duration (under the assumption that the tick will be stopped) and deciding whether or not it makes sense to stop the tick before putting the CPU into the selected idle state. With the above, the sleep_length field in struct tick_sched is not necessary any more, so drop it. Link: https://bugzilla.kernel.org/show_bug.cgi?id=199227 Reported-by: Doug Smythies <dsmythies@telus.net> Reported-by: Thomas Ilsche <thomas.ilsche@tu-dresden.de> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Diffstat (limited to 'include/linux/tick.h')
-rw-r--r--include/linux/tick.h2
1 files changed, 2 insertions, 0 deletions
diff --git a/include/linux/tick.h b/include/linux/tick.h
index ef0717e5e526..e8e7ff16b929 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -116,6 +116,7 @@ extern bool tick_nohz_enabled;
extern bool tick_nohz_tick_stopped(void);
extern bool tick_nohz_tick_stopped_cpu(int cpu);
extern void tick_nohz_idle_stop_tick(void);
+extern void tick_nohz_idle_retain_tick(void);
extern void tick_nohz_idle_restart_tick(void);
extern void tick_nohz_idle_enter(void);
extern void tick_nohz_idle_exit(void);
@@ -139,6 +140,7 @@ static inline void tick_nohz_idle_stop_tick_protected(void)
static inline int tick_nohz_tick_stopped(void) { return 0; }
static inline int tick_nohz_tick_stopped_cpu(int cpu) { return 0; }
static inline void tick_nohz_idle_stop_tick(void) { }
+static inline void tick_nohz_idle_retain_tick(void) { }
static inline void tick_nohz_idle_restart_tick(void) { }
static inline void tick_nohz_idle_enter(void) { }
static inline void tick_nohz_idle_exit(void) { }