@@ -188,6 +188,8 @@ static inline unsigned long tb_ticks_since(unsigned long tstamp)
extern u64 mulhdu(u64, u64);
#endif
+extern bool try_set_dec_before_idle(u64 timeout);
+extern void try_reset_dec_after_idle(void);
extern void div128_by_32(u64 dividend_high, u64 dividend_low,
unsigned divisor, struct div_result *dr);
@@ -576,6 +576,49 @@ void arch_irq_work_raise(void)
#endif /* CONFIG_IRQ_WORK */
+/*
+ * This function tries setting decrementer before entering into idle.
+ * Returns true if we have reprogrammed the decrementer for idle.
+ * Returns false if the decrementer is unchanged.
+ */
+bool try_set_dec_before_idle(u64 timeout)
+{
+ u64 *next_tb = this_cpu_ptr(&decrementers_next_tb);
+ u64 now = get_tb_or_rtc();
+
+ if (now + timeout > *next_tb)
+ return false;
+
+ set_dec(timeout);
+ if (test_irq_work_pending())
+ set_dec(1);
+
+ return true;
+}
+
+/*
+ * This function gets called if we have set decrementer before
+ * entering into idle. It tries to reset/restore the decrementer
+ * to its original value.
+ */
+void try_reset_dec_after_idle(void)
+{
+ u64 now;
+ u64 *next_tb;
+
+ if (test_irq_work_pending())
+ return;
+
+ now = get_tb_or_rtc();
+ next_tb = this_cpu_ptr(&decrementers_next_tb);
+ if (now >= *next_tb)
+ return;
+
+ set_dec(*next_tb - now);
+ if (test_irq_work_pending())
+ set_dec(1);
+}
+
/*
* timer_interrupt - gets called when the decrementer overflows,
* with interrupts disabled.
@@ -21,6 +21,7 @@
#include <asm/opal.h>
#include <asm/runlatch.h>
#include <asm/cpuidle.h>
+#include <asm/time.h>
/*
* Expose only those Hardware idle states via the cpuidle framework
@@ -46,6 +47,26 @@ static struct stop_psscr_table stop_psscr_table[CPUIDLE_STATE_MAX] __read_mostly
static u64 default_snooze_timeout __read_mostly;
static bool snooze_timeout_en __read_mostly;
+static u64 forced_wakeup_timeout(struct cpuidle_device *dev,
+ struct cpuidle_driver *drv,
+ int index)
+{
+ int i;
+
+ for (i = index + 1; i < drv->state_count; i++) {
+ struct cpuidle_state *s = &drv->states[i];
+ struct cpuidle_state_usage *su = &dev->states_usage[i];
+
+ if (s->disabled || su->disable)
+ continue;
+
+ return (s->target_residency + 2 * s->exit_latency) *
+ tb_ticks_per_usec;
+ }
+
+ return 0;
+}
+
static u64 get_snooze_timeout(struct cpuidle_device *dev,
struct cpuidle_driver *drv,
int index)
@@ -144,8 +165,27 @@ static int stop_loop(struct cpuidle_device *dev,
struct cpuidle_driver *drv,
int index)
{
+ u64 timeout_tb;
+ bool forced_wakeup = false;
+
+ timeout_tb = forced_wakeup_timeout(dev, drv, index);
+
+ /* Ensure that the timeout is at least one microsecond
+ * greater than current decrement value. Else, we will
+ * unnecesarily wakeup again within a microsecond if we
+ * set decrementer with such timeout value.
+ */
+ timeout_tb += 512;
+
+ if (timeout_tb)
+ forced_wakeup = try_set_dec_before_idle(timeout_tb);
+
power9_idle_type(stop_psscr_table[index].val,
stop_psscr_table[index].mask);
+
+ if (forced_wakeup)
+ try_reset_dec_after_idle();
+
return index;
}
Currently, the cpuidle governors determine what idle state a idling CPU should enter into based on heuristics that depend on the idle history on that CPU. Given that no predictive heuristic is perfect, there are cases where the governor predicts a shallow idle state, hoping that the CPU will be busy soon. However, if no new workload is scheduled on that CPU in the near future, the CPU may end up in the shallow state. This is problematic, when the predicted state in the aforementioned scenario is a shallow stop state on a tickless system. As we might get stuck into shallow states for hours, in absence of ticks or interrupts. To address this, We forcefully wakeup the cpu by setting the decrementer. The decrementer is set to a value that corresponds with the residency of the next available state. Thus firing up a timer that will forcefully wakeup the cpu. Few such iterations will essentially train the governor to select a deeper state for that cpu, as the timer here corresponds to the next available cpuidle state residency. Thus, cpu will eventually end up in the deepest possible state. Signed-off-by: Abhishek Goel <huntbag@linux.vnet.ibm.com> --- Auto-promotion v1 : started as auto promotion logic for cpuidle states in generic driver v2 : Removed timeout_needed and rebased the code to upstream kernel Forced-wakeup v1 : New patch with name of forced wakeup started v2 : Extending the forced wakeup logic for all states. Setting the decrementer instead of queuing up a hrtimer to implement the logic. v3 : Cleanly handle setting/resetting of decrementer so as to not break irq work v4 : Changed type and name of set/reset decrementer fucntion Handled irq_work_pending in try_set_dec_before_idle arch/powerpc/include/asm/time.h | 2 ++ arch/powerpc/kernel/time.c | 43 +++++++++++++++++++++++++++++++ drivers/cpuidle/cpuidle-powernv.c | 40 ++++++++++++++++++++++++++++ 3 files changed, 85 insertions(+)