f27dde8dee
In order to combine the preemption and need_resched test we need to
fold the need_resched information into the preempt_count value.
Since the NEED_RESCHED flag is set across CPUs this needs to be an
atomic operation, however we very much want to avoid making
preempt_count atomic, therefore we keep the existing TIF_NEED_RESCHED
infrastructure in place but at 3 sites test it and fold its value into
preempt_count; namely:
- resched_task() when setting TIF_NEED_RESCHED on the current task
- scheduler_ipi() when resched_task() sets TIF_NEED_RESCHED on a
remote task it follows it up with a reschedule IPI
and we can modify the cpu local preempt_count from
there.
- cpu_idle_loop() for when resched_task() found tsk_is_polling().
We use an inverted bitmask to indicate need_resched so that a 0 means
both need_resched and !atomic.
Also remove the barrier() in preempt_enable() between
preempt_enable_no_resched() and preempt_check_resched() to avoid
having to reload the preemption value and allow the compiler to use
the flags of the previuos decrement. I couldn't come up with any sane
reason for this barrier() to be there as preempt_enable_no_resched()
already has a barrier() before doing the decrement.
Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-7a7m5qqbn5pmwnd4wko9u6da@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
142 lines
3.2 KiB
C
142 lines
3.2 KiB
C
/*
|
|
* Generic entry point for the idle threads
|
|
*/
|
|
#include <linux/sched.h>
|
|
#include <linux/cpu.h>
|
|
#include <linux/tick.h>
|
|
#include <linux/mm.h>
|
|
#include <linux/stackprotector.h>
|
|
|
|
#include <asm/tlb.h>
|
|
|
|
#include <trace/events/power.h>
|
|
|
|
static int __read_mostly cpu_idle_force_poll;
|
|
|
|
void cpu_idle_poll_ctrl(bool enable)
|
|
{
|
|
if (enable) {
|
|
cpu_idle_force_poll++;
|
|
} else {
|
|
cpu_idle_force_poll--;
|
|
WARN_ON_ONCE(cpu_idle_force_poll < 0);
|
|
}
|
|
}
|
|
|
|
#ifdef CONFIG_GENERIC_IDLE_POLL_SETUP
|
|
static int __init cpu_idle_poll_setup(char *__unused)
|
|
{
|
|
cpu_idle_force_poll = 1;
|
|
return 1;
|
|
}
|
|
__setup("nohlt", cpu_idle_poll_setup);
|
|
|
|
static int __init cpu_idle_nopoll_setup(char *__unused)
|
|
{
|
|
cpu_idle_force_poll = 0;
|
|
return 1;
|
|
}
|
|
__setup("hlt", cpu_idle_nopoll_setup);
|
|
#endif
|
|
|
|
static inline int cpu_idle_poll(void)
|
|
{
|
|
rcu_idle_enter();
|
|
trace_cpu_idle_rcuidle(0, smp_processor_id());
|
|
local_irq_enable();
|
|
while (!tif_need_resched())
|
|
cpu_relax();
|
|
trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
|
|
rcu_idle_exit();
|
|
return 1;
|
|
}
|
|
|
|
/* Weak implementations for optional arch specific functions */
|
|
void __weak arch_cpu_idle_prepare(void) { }
|
|
void __weak arch_cpu_idle_enter(void) { }
|
|
void __weak arch_cpu_idle_exit(void) { }
|
|
void __weak arch_cpu_idle_dead(void) { }
|
|
void __weak arch_cpu_idle(void)
|
|
{
|
|
cpu_idle_force_poll = 1;
|
|
local_irq_enable();
|
|
}
|
|
|
|
/*
|
|
* Generic idle loop implementation
|
|
*/
|
|
static void cpu_idle_loop(void)
|
|
{
|
|
while (1) {
|
|
tick_nohz_idle_enter();
|
|
|
|
while (!need_resched()) {
|
|
check_pgt_cache();
|
|
rmb();
|
|
|
|
if (cpu_is_offline(smp_processor_id()))
|
|
arch_cpu_idle_dead();
|
|
|
|
local_irq_disable();
|
|
arch_cpu_idle_enter();
|
|
|
|
/*
|
|
* In poll mode we reenable interrupts and spin.
|
|
*
|
|
* Also if we detected in the wakeup from idle
|
|
* path that the tick broadcast device expired
|
|
* for us, we don't want to go deep idle as we
|
|
* know that the IPI is going to arrive right
|
|
* away
|
|
*/
|
|
if (cpu_idle_force_poll || tick_check_broadcast_expired()) {
|
|
cpu_idle_poll();
|
|
} else {
|
|
if (!current_clr_polling_and_test()) {
|
|
stop_critical_timings();
|
|
rcu_idle_enter();
|
|
arch_cpu_idle();
|
|
WARN_ON_ONCE(irqs_disabled());
|
|
rcu_idle_exit();
|
|
start_critical_timings();
|
|
} else {
|
|
local_irq_enable();
|
|
}
|
|
__current_set_polling();
|
|
}
|
|
arch_cpu_idle_exit();
|
|
/*
|
|
* We need to test and propagate the TIF_NEED_RESCHED
|
|
* bit here because we might not have send the
|
|
* reschedule IPI to idle tasks.
|
|
*/
|
|
if (tif_need_resched())
|
|
set_preempt_need_resched();
|
|
}
|
|
tick_nohz_idle_exit();
|
|
schedule_preempt_disabled();
|
|
}
|
|
}
|
|
|
|
void cpu_startup_entry(enum cpuhp_state state)
|
|
{
|
|
/*
|
|
* This #ifdef needs to die, but it's too late in the cycle to
|
|
* make this generic (arm and sh have never invoked the canary
|
|
* init for the non boot cpus!). Will be fixed in 3.11
|
|
*/
|
|
#ifdef CONFIG_X86
|
|
/*
|
|
* If we're the non-boot CPU, nothing set the stack canary up
|
|
* for us. The boot CPU already has it initialized but no harm
|
|
* in doing it again. This is a good place for updating it, as
|
|
* we wont ever return from this function (so the invalid
|
|
* canaries already on the stack wont ever trigger).
|
|
*/
|
|
boot_init_stack_canary();
|
|
#endif
|
|
__current_set_polling();
|
|
arch_cpu_idle_prepare();
|
|
cpu_idle_loop();
|
|
}
|