851d14afc8
The scheduler has historically had an API where an application can inform the kernel that it will never create a thread that can be preempted, and the kernel and architecture layer would use that as an optimization hint to eliminate some code paths. Those optimizations have dwindled to almost nothing at this point, and they're now objectively a smaller impact than the special casing that was required to handle the idle thread (which, obviously, must always be preemptible). Fix this by eliminating the idea of "cooperative only" and ensuring that there will always be at least one preemptible priority with value >=0. CONFIG_NUM_PREEMPT_PRIORITIES now specifies the number of user-accessible priorities other than the idle thread. The only remaining workaround is that some older architectures (and also SPARC) use the CONFIG_PREEMPT_ENABLED=n state as a hint to skip thread switching on interrupt exit. So detect exactly those platforms and implement a minimal workaround in the idle loop (basically "just call swap()") instead, with a big explanation. Note that this also fixes a bug in one of the philosophers samples, where it would ask for 6 cooperative priorities but then use values -7 through -2. It was assuming the kernel would magically create a cooperative priority for its idle thread, which wasn't correct even before. Fixes #34584 Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
118 lines
3.2 KiB
C
118 lines
3.2 KiB
C
/*
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* Copyright (c) 2016 Wind River Systems, Inc.
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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#include <kernel.h>
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#include <toolchain.h>
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#include <linker/sections.h>
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#include <drivers/timer/system_timer.h>
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#include <wait_q.h>
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#include <pm/pm.h>
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#include <stdbool.h>
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#include <logging/log.h>
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#include <ksched.h>
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#include <kswap.h>
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LOG_MODULE_DECLARE(os, CONFIG_KERNEL_LOG_LEVEL);
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/**
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* @brief Indicate that kernel is idling in tickless mode
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*
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* Sets the kernel data structure idle field to either a positive value or
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* K_FOREVER.
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*/
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static void pm_save_idle(void)
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{
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#ifdef CONFIG_PM
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int32_t ticks = z_get_next_timeout_expiry();
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_kernel.idle = ticks;
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/*
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* Call the suspend hook function of the soc interface to allow
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* entry into a low power state. The function returns
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* PM_STATE_ACTIVE if low power state was not entered, in which
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* case, kernel does normal idle processing.
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*
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* This function is entered with interrupts disabled. If a low power
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* state was entered, then the hook function should enable inerrupts
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* before exiting. This is because the kernel does not do its own idle
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* processing in those cases i.e. skips k_cpu_idle(). The kernel's
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* idle processing re-enables interrupts which is essential for
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* the kernel's scheduling logic.
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*/
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if (pm_system_suspend(ticks) == PM_STATE_ACTIVE) {
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k_cpu_idle();
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}
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#endif
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}
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void z_pm_save_idle_exit(int32_t ticks)
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{
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#ifdef CONFIG_PM
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/* Some CPU low power states require notification at the ISR
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* to allow any operations that needs to be done before kernel
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* switches task or processes nested interrupts.
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* This can be simply ignored if not required.
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*/
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pm_system_resume();
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#endif /* CONFIG_PM */
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sys_clock_idle_exit();
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}
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void idle(void *unused1, void *unused2, void *unused3)
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{
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ARG_UNUSED(unused1);
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ARG_UNUSED(unused2);
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ARG_UNUSED(unused3);
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__ASSERT_NO_MSG(_current->base.prio >= 0);
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while (true) {
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/* SMP systems without a working IPI can't
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* actual enter an idle state, because they
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* can't be notified of scheduler changes
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* (i.e. threads they should run). They just
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* spin in a yield loop. This is intended as
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* a fallback configuration for new platform
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* bringup.
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*/
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if (IS_ENABLED(CONFIG_SMP) &&
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!IS_ENABLED(CONFIG_SCHED_IPI_SUPPORTED)) {
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k_busy_wait(100);
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k_yield();
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continue;
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}
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/* Note weird API: k_cpu_idle() is called with local
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* CPU interrupts masked, and returns with them
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* unmasked. It does not take a spinlock or other
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* higher level construct.
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*/
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(void) arch_irq_lock();
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if (IS_ENABLED(CONFIG_PM)) {
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pm_save_idle();
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} else {
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k_cpu_idle();
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}
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#if !defined(CONFIG_PREEMPT_ENABLED)
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# if !defined(CONFIG_USE_SWITCH) || defined(CONFIG_SPARC)
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/* A legacy mess: the idle thread is by definition
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* preemptible as far as the modern scheduler is
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* concerned, but older platforms use
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* CONFIG_PREEMPT_ENABLED=n as an optimization hint
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* that interrupt exit always returns to the
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* interrupted context. So in that setup we need to
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* explicitly yield in the idle thread otherwise
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* nothing else will run once it starts.
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*/
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if (_kernel.ready_q.cache != _current) {
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z_swap_unlocked();
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}
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# endif
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#endif
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}
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}
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