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switch to idle_host_task when idle #336

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Mar 5, 2017
Merged

switch to idle_host_task when idle #336

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88f8dc2
switch to idle_host_task when idle
laijs Feb 22, 2017
2545621
don't leave cpu if there is any running task
laijs Feb 25, 2017
a7d380d
revert 9072b9a ("lkl: expose cpu_idle_loop from idle.c")
laijs Mar 5, 2017
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4 changes: 0 additions & 4 deletions arch/lkl/include/asm/cpu.h
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Original file line number Diff line number Diff line change
Expand Up @@ -7,11 +7,7 @@ int lkl_cpu_try_run_irq(int irq);
int lkl_cpu_init(void);
void lkl_cpu_shutdown(void);
void lkl_cpu_wait_shutdown(void);
void lkl_cpu_wakeup_idle(void);
void lkl_cpu_change_owner(lkl_thread_t owner);
void lkl_cpu_set_irqs_pending(void);
void lkl_idle_tail_schedule(void);
int lkl_cpu_idle_pending(void);
extern void do_idle(void);

#endif /* _ASM_LKL_CPU_H */
9 changes: 4 additions & 5 deletions arch/lkl/include/asm/sched.h
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Original file line number Diff line number Diff line change
Expand Up @@ -2,18 +2,17 @@
#define _ASM_LKL_SCHED_H

#include <linux/sched.h>
#include <uapi/asm/host_ops.h>

static inline void thread_sched_jb(void)
{
set_ti_thread_flag(current_thread_info(), TIF_SCHED_JB);

if (test_ti_thread_flag(current_thread_info(), TIF_HOST_THREAD)) {
set_ti_thread_flag(current_thread_info(), TIF_SCHED_JB);
set_current_state(TASK_UNINTERRUPTIBLE);
lkl_ops->jmp_buf_set(&current_thread_info()->sched_jb,
schedule);
} else {
lkl_ops->jmp_buf_set(&current_thread_info()->sched_jb,
lkl_idle_tail_schedule);
} else {
lkl_bug("thread_sched_jb() can be used only for host task");
}
}

Expand Down
1 change: 1 addition & 0 deletions arch/lkl/include/asm/syscalls.h
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
int syscalls_init(void);
void syscalls_cleanup(void);
long lkl_syscall(long no, long *params);
void wakeup_idle_host_task(void);

#define sys_mmap sys_mmap_pgoff
#define sys_mmap2 sys_mmap_pgoff
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1 change: 0 additions & 1 deletion arch/lkl/include/asm/thread_info.h
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Original file line number Diff line number Diff line change
Expand Up @@ -59,7 +59,6 @@ void threads_cleanup(void);
#define TIF_NOHZ 6
#define TIF_SCHED_JB 7
#define TIF_HOST_THREAD 8
#define TIF_IDLE 9

#define __HAVE_THREAD_FUNCTIONS

Expand Down
91 changes: 5 additions & 86 deletions arch/lkl/kernel/cpu.c
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Original file line number Diff line number Diff line change
@@ -1,8 +1,5 @@
#include <linux/cpu.h>
#include <linux/cpuidle.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/tick.h>
#include <asm/host_ops.h>
#include <asm/cpu.h>
#include <asm/thread_info.h>
Expand Down Expand Up @@ -52,12 +49,6 @@ struct lkl_cpu {
lkl_thread_t owner;
/* semaphore for threads waiting the CPU */
struct lkl_sem *sem;
/* semaphore for the idle thread */
struct lkl_sem *idle_sem;
/* if the idle thread is pending */
bool idle_pending;
/* jmp_buf used for idle thread to restart */
struct lkl_jmp_buf idle_jb;
/* semaphore used for shutdown */
struct lkl_sem *shutdown_sem;
} cpu;
Expand Down Expand Up @@ -134,7 +125,8 @@ void lkl_cpu_put(void)
lkl_ops->mutex_lock(cpu.lock);
}

if (need_resched() && cpu.count == 1) {
if (test_ti_thread_flag(current_thread_info(), TIF_HOST_THREAD) &&
need_resched() && cpu.count == 1) {
if (in_interrupt())
lkl_bug("%s: in interrupt\n", __func__);
lkl_ops->mutex_unlock(cpu.lock);
Expand Down Expand Up @@ -191,8 +183,6 @@ static void lkl_cpu_cleanup(bool shutdown)
lkl_ops->sem_up(cpu.shutdown_sem);
else if (cpu.shutdown_sem)
lkl_ops->sem_free(cpu.shutdown_sem);
if (cpu.idle_sem)
lkl_ops->sem_free(cpu.idle_sem);
if (cpu.sem)
lkl_ops->sem_free(cpu.sem);
if (cpu.lock)
Expand All @@ -215,91 +205,20 @@ void arch_cpu_idle(void)
/* enable irqs now to allow direct irqs to run */
local_irq_enable();

if (need_resched())
return;

cpu.idle_pending = true;
lkl_cpu_put();

lkl_ops->sem_down(cpu.idle_sem);

cpu.idle_pending = false;
/* to match that of schedule_preempt_disabled() */
preempt_disable();
lkl_ops->jmp_buf_longjmp(&cpu.idle_jb, 1);
}

void arch_cpu_idle_prepare(void)
{
set_ti_thread_flag(current_thread_info(), TIF_IDLE);
/*
* We hijack the idle loop here so that we can let the idle thread
* jump back to the beginning.
*/
while (1)
lkl_ops->jmp_buf_set(&cpu.idle_jb, do_idle);
}

void lkl_cpu_wakeup_idle(void)
{
lkl_ops->sem_up(cpu.idle_sem);
/* switch to idle_host_task */
wakeup_idle_host_task();
}

int lkl_cpu_init(void)
{
cpu.lock = lkl_ops->mutex_alloc(0);
cpu.sem = lkl_ops->sem_alloc(0);
cpu.idle_sem = lkl_ops->sem_alloc(0);
cpu.shutdown_sem = lkl_ops->sem_alloc(0);

if (!cpu.lock || !cpu.sem || !cpu.idle_sem || !cpu.shutdown_sem) {
if (!cpu.lock || !cpu.sem || !cpu.shutdown_sem) {
lkl_cpu_cleanup(false);
return -ENOMEM;
}

return 0;
}

/*
* Simulate the exit path of idle loop so that we can schedule when LKL is
* in idle.
* It's just a duplication of those in idle.c so a better way is to refactor
* idle.c to expose such function.
*/
void lkl_idle_tail_schedule(void)
{

if (!cpu.idle_pending ||
!test_bit(TIF_IDLE, &current_thread_info()->flags))
lkl_bug("%s: not in idle\n", __func__);

start_critical_timings();
__current_set_polling();

if (WARN_ON_ONCE(irqs_disabled()))
local_irq_enable();

rcu_idle_exit();
arch_cpu_idle_exit();
preempt_set_need_resched();
tick_nohz_idle_exit();
__current_clr_polling();

/*
* memory barrier copied from idle.c
*/
smp_mb__after_atomic();

/*
* Didn't find a way to include kernel/sched/sched.h for
* sched_ttwu_pending().
* Anyway, it's no op when not CONFIG_SMP.
*/

schedule_preempt_disabled();
}

int lkl_cpu_idle_pending(void)
{
return cpu.idle_pending;
}
42 changes: 42 additions & 0 deletions arch/lkl/kernel/syscalls.c
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Original file line number Diff line number Diff line change
Expand Up @@ -130,6 +130,34 @@ long lkl_syscall(long no, long *params)
return ret;
}

static struct task_struct *idle_host_task;

/* called from idle, don't failed, don't block */
void wakeup_idle_host_task(void)
{
if (!need_resched() && idle_host_task)
wake_up_process(idle_host_task);
}

static int idle_host_task_loop(void *unused)
{
struct thread_info *ti = task_thread_info(current);

snprintf(current->comm, sizeof(current->comm), "idle_host_task");
set_thread_flag(TIF_HOST_THREAD);
idle_host_task = current;

for (;;) {
lkl_cpu_put();
lkl_ops->sem_down(ti->sched_sem);
if (idle_host_task == NULL) {
lkl_ops->thread_exit();
return 0;
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Not needed

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the compiler will warn on it if it is removed.

}
schedule_tail(ti->prev_sched);
}
}

int syscalls_init(void)
{
snprintf(current->comm, sizeof(current->comm), "host0");
Expand All @@ -142,11 +170,25 @@ int syscalls_init(void)
return -1;
}

if (kernel_thread(idle_host_task_loop, NULL, CLONE_FLAGS) < 0) {
if (lkl_ops->tls_free)
lkl_ops->tls_free(task_key);
return -1;
}

return 0;
}

void syscalls_cleanup(void)
{
if (idle_host_task) {
struct thread_info *ti = task_thread_info(idle_host_task);

idle_host_task = NULL;
lkl_ops->sem_up(ti->sched_sem);
lkl_ops->thread_join(ti->tid);
}

if (lkl_ops->tls_free)
lkl_ops->tls_free(task_key);
}
Expand Down
13 changes: 2 additions & 11 deletions arch/lkl/kernel/threads.c
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Original file line number Diff line number Diff line change
Expand Up @@ -89,31 +89,22 @@ struct task_struct *__switch_to(struct task_struct *prev,
struct thread_info *_prev = task_thread_info(prev);
struct thread_info *_next = task_thread_info(next);
unsigned long _prev_flags = _prev->flags;
bool wakeup_idle = test_bit(TIF_IDLE, &_next->flags) &&
lkl_cpu_idle_pending();
struct lkl_jmp_buf _prev_jb;

_current_thread_info = task_thread_info(next);
_next->prev_sched = prev;
abs_prev = prev;

BUG_ON(!_next->tid);
lkl_cpu_change_owner(_next->tid);

if (test_bit(TIF_SCHED_JB, &_prev_flags)) {
/* Atomic. Must be done before wakeup next */
clear_ti_thread_flag(_prev, TIF_SCHED_JB);
_prev_jb = _prev->sched_jb;
}
if (wakeup_idle)
schedule_tail(abs_prev);
lkl_cpu_change_owner(_next->tid);

/* No kernel code is allowed after wakeup next */
if (wakeup_idle)
lkl_cpu_wakeup_idle();
else
lkl_ops->sem_up(_next->sched_sem);

lkl_ops->sem_up(_next->sched_sem);
if (test_bit(TIF_SCHED_JB, &_prev_flags)) {
lkl_ops->jmp_buf_longjmp(&_prev_jb, 1);
} else {
Expand Down