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idle: Fix tickless timeout behavior

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If the idle code was detecting that it needed to sleep for less than
CONFIG_SYS_TICKLESS_IDLE_THRESH, then it would never call
z_clock_set_timeout() at all, which means that the system would never
wake up unless it already had a timeout scheduled!  Apparently we
lacked a test case to detect this condition.

Honestly this seems like a crazy feature to me.  There's no benefit in
delivering needless tick announcements.  If the system has the
capacity to enter deeper sleep for long timeouts, that's already
exposed via the PM APIs, the timer subsystem needn't be involved.
But... we actually have a test (tickless_concept) that looks at this,
so support it for now and consider deprecation later.

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
This commit is contained in:
Andy Ross 2018-09-22 09:01:52 -07:00 committed by Anas Nashif
parent d7b35c9bd6
commit 7aae75bd1c
2 changed files with 17 additions and 32 deletions
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42
kernel/idle.c
View file

@ -13,22 +13,11 @@
#include <power.h>
#include <stdbool.h>
#if defined(CONFIG_TICKLESS_IDLE)
/*
* Idle time must be this value or higher for timer to go into tickless idle
* state.
*/
s32_t _sys_idle_threshold_ticks = CONFIG_TICKLESS_IDLE_THRESH;
#if defined(CONFIG_TICKLESS_KERNEL)
#define _must_enter_tickless_idle(ticks) (true)
#ifdef CONFIG_TICKLESS_IDLE_THRESH
#define IDLE_THRESH CONFIG_TICKLESS_IDLE_THRESH
#else
#define _must_enter_tickless_idle(ticks) \
((ticks == K_FOREVER) || (ticks >= _sys_idle_threshold_ticks))
#define IDLE_THRESH 1
#endif
#else
#define _must_enter_tickless_idle(ticks) ((void)ticks, false)
#endif /* CONFIG_TICKLESS_IDLE */
#ifdef CONFIG_SYS_POWER_MANAGEMENT
/*
@ -70,19 +59,13 @@ static void set_kernel_idle_time_in_ticks(s32_t ticks)
#ifndef CONFIG_SMP
static void sys_power_save_idle(s32_t ticks)
{
if (_must_enter_tickless_idle(ticks)) {
/*
* Stop generating system timer interrupts until it's time for
* the next scheduled kernel timer to expire.
*/
/*
* In the case of tickless kernel, timer driver should
* reprogram timer only if the currently programmed time
* duration is smaller than the idle time.
*/
z_clock_set_timeout(ticks, true);
}
/* 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_clock_set_timeout(ticks < IDLE_THRESH ? 1 : ticks, true);
set_kernel_idle_time_in_ticks(ticks);
#if (defined(CONFIG_SYS_POWER_LOW_POWER_STATE) || \
@ -127,10 +110,7 @@ void _sys_power_save_idle_exit(s32_t ticks)
}
#endif
if (_must_enter_tickless_idle(ticks)) {
/* Resume normal periodic system timer interrupts */
z_clock_idle_exit();
}
z_clock_idle_exit();
}

7
tests/kernel/tickless/tickless/src/main.c
View file

@ -27,7 +27,12 @@ static struct k_thread thread_tickless;
static K_THREAD_STACK_DEFINE(thread_tickless_stack, STACKSIZE);
#ifdef CONFIG_TICKLESS_IDLE
extern s32_t _sys_idle_threshold_ticks;
/* This used to poke an internal kernel variable, which doesn't exit
* any more. It was never documented as an API, and the test never
* failed when it was removed. So just leave it here as a vestigial
* thing until the test gets reworked
*/
s32_t _sys_idle_threshold_ticks;
#endif
#define TICKS_TO_MS (MSEC_PER_SEC / CONFIG_SYS_CLOCK_TICKS_PER_SEC)