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kernel/idle: Clean up and refactoring / remove TICKLESS_IDLE_THRESH

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While I'm in the idle code, let's clean this loop up.  It was a really
bad #ifdef hell:

* Remove the CONFIG_TICKLESS_IDLE_THRESH logic (and the kconfig),
  which never did anything but needlessly increase latency.

* Move the needed timeout logic from the main loop into
  pm_save_idle(), which eliminates the special case for
  !SYS_CLOCK_EXISTS.

Behavior (modulo that one kconfig) should be completely unchanged, and
now the inner part of the idle loop looks like:

    while (true) {
        (void) arch_irq_lock();

        if (IS_ENABLED(CONFIG_PM)) {
            pm_save_idle();
        } else {
            k_cpu_idle();
        }
    }

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
This commit is contained in:
Andy Ross 2021-03-03 13:20:15 -08:00 • committed by Anas Nashif
commit 6400bb54d6
2 changed files with 44 additions and 81 deletions
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10
kernel/Kconfig
View file

@ -852,16 +852,6 @@ config TICKLESS_IDLE
saving state for extended periods without having to wake up to
service each tick as it occurs.
config TICKLESS_IDLE_THRESH
int "Tickless idle threshold"
default 3
depends on TICKLESS_IDLE
help
This option enables clock interrupt suppression when the kernel idles
for only a short period of time. It specifies the minimum number of
ticks that must occur before the next kernel timer expires in order
for suppression to happen.
config TICKLESS_KERNEL
bool "Tickless kernel"
default y if TICKLESS_CAPABLE

115
kernel/idle.c
View file

@ -14,21 +14,10 @@
#include <logging/log.h>
#include <ksched.h>
extern uint32_t z_timestamp_idle;
LOG_MODULE_DECLARE(os, CONFIG_KERNEL_LOG_LEVEL);
#ifdef CONFIG_TICKLESS_IDLE_THRESH
#define IDLE_THRESH CONFIG_TICKLESS_IDLE_THRESH
#else
#define IDLE_THRESH 1
#endif
/* Fallback idle spin loop for SMP platforms without a working IPI */
#if (defined(CONFIG_SMP) && !defined(CONFIG_SCHED_IPI_SUPPORTED))
#define SMP_FALLBACK 1
#else
#define SMP_FALLBACK 0
#endif
#ifdef CONFIG_PM
/*
* Used to allow pm_system_suspend() implementation to control notification
@ -36,7 +25,6 @@ LOG_MODULE_DECLARE(os, CONFIG_KERNEL_LOG_LEVEL);
*/
unsigned char pm_idle_exit_notify;
/* LCOV_EXCL_START
* These are almost certainly overidden and in any event do nothing
*/
@ -52,20 +40,16 @@ void __attribute__((weak)) pm_system_resume_from_deep_sleep(void)
#endif /* CONFIG_PM */
/**
*
* @brief Indicate that kernel is idling in tickless mode
*
* Sets the kernel data structure idle field to either a positive value or
* K_FOREVER.
*
* @param ticks the number of ticks to idle
*
* @return N/A
*/
#if !SMP_FALLBACK && CONFIG_PM
static enum pm_state pm_save_idle(int32_t ticks)
static void pm_save_idle(void)
{
static enum pm_state idle_state = PM_STATE_ACTIVE;
#ifdef CONFIG_PM
int32_t ticks = z_get_next_timeout_expiry();
_kernel.idle = ticks;
pm_idle_exit_notify = 1U;
@ -82,16 +66,12 @@ static enum pm_state pm_save_idle(int32_t ticks)
* idle processing re-enables interrupts which is essential for
* the kernel's scheduling logic.
*/
idle_state = pm_system_suspend(ticks);
if (idle_state == PM_STATE_ACTIVE) {
if (pm_system_suspend(ticks) == PM_STATE_ACTIVE) {
pm_idle_exit_notify = 0U;
k_cpu_idle();
}
return idle_state;
#endif
}
#endif /* !SMP_FALLBACK */
void z_pm_save_idle_exit(int32_t ticks)
{
@ -105,64 +85,57 @@ void z_pm_save_idle_exit(int32_t ticks)
if (pm_idle_exit_notify) {
pm_system_resume();
}
#endif /* CONFIG_PM */
#endif
z_clock_idle_exit();
}
#if K_IDLE_PRIO < 0
#define IDLE_YIELD_IF_COOP() k_yield()
#else
#define IDLE_YIELD_IF_COOP() do { } while (false)
#endif
void idle(void *p1, void *unused2, void *unused3)
void idle(void *unused1, void *unused2, void *unused3)
{
ARG_UNUSED(unused1);
ARG_UNUSED(unused2);
ARG_UNUSED(unused3);
#ifdef CONFIG_BOOT_TIME_MEASUREMENT
/* record timestamp when idling begins */
extern uint32_t z_timestamp_idle;
z_timestamp_idle = k_cycle_get_32();
#endif /* CONFIG_BOOT_TIME_MEASUREMENT */
#endif
while (true) {
#if SMP_FALLBACK
k_busy_wait(100);
k_yield();
#else
/* SMP systems without a working IPI can't
* actual enter an idle state, because they
* can't be notified of scheduler changes
* (i.e. threads they should run). They just
* spin in a yield loop. This is intended as
* a fallback configuration for new platform
* bringup.
*/
if (IS_ENABLED(CONFIG_SMP) &&
!IS_ENABLED(CONFIG_SCHED_IPI_SUPPORTED)) {
k_busy_wait(100);
k_yield();
continue;
}
/* Note weird API: k_cpu_idle() is called with local
* CPU interrupts masked, and returns with them
* unmasked. It does not take a spinlock or other
* higher level construct.
*/
(void) arch_irq_lock();
#ifdef CONFIG_SYS_CLOCK_EXISTS
int32_t ticks = z_get_next_timeout_expiry();
/* The documented behavior of CONFIG_TICKLESS_IDLE_THRESH is
* that the system should not enter a tickless idle for
* periods less than that. This seems... silly, given that it
* saves no power and does not improve latency. But it's an
* API we need to honor...
*/
z_set_timeout_expiry((ticks < IDLE_THRESH) ? 1 : ticks, true);
#ifdef CONFIG_PM
_kernel.idle = ticks;
/* Check power policy and decide if we are going to sleep or
* just idle.
*/
if (pm_save_idle(ticks) == PM_STATE_ACTIVE) {
if (IS_ENABLED(CONFIG_PM)) {
pm_save_idle();
} else {
k_cpu_idle();
}
#else /* CONFIG_PM */
k_cpu_idle();
#endif /* CONFIG_PM */
#else /* CONFIG_SYS_CLOCK_EXISTS */
k_cpu_idle();
#endif /* CONFIG_SYS_CLOCK_EXISTS */
IDLE_YIELD_IF_COOP();
#endif /* SMP_FALLBACK */
/* It is possible to (pathologically) configure the
* idle thread to have a non-preemptible priority.
* You might think this is an API bug, but we actually
* have a test that exercises this. Handle the edge
* case when that happens.
*/
if (K_IDLE_PRIO < 0) {
k_yield();
}
}
}