#include <linux/sched.h>
#include <litmus/litmus.h>
#include <litmus/preempt.h>
/* The rescheduling state of each processor.
*/
DEFINE_PER_CPU_SHARED_ALIGNED(atomic_t, resched_state);
void sched_state_will_schedule(struct task_struct* tsk)
{
/* Litmus hack: we only care about processor-local invocations of
* set_tsk_need_resched(). We can't reliably set the flag remotely
* since it might race with other updates to the scheduling state. We
* can't rely on the runqueue lock protecting updates to the sched
* state since processors do not acquire the runqueue locks for all
* updates to the sched state (to avoid acquiring two runqueue locks at
* the same time). Further, if tsk is residing on a remote processor,
* then that processor doesn't actually know yet that it is going to
* reschedule; it still must receive an IPI (unless a local invocation
* races).
*/
if (likely(task_cpu(tsk) == smp_processor_id())) {
VERIFY_SCHED_STATE(TASK_SCHEDULED | SHOULD_SCHEDULE | TASK_PICKED | WILL_SCHEDULE);
if (is_in_sched_state(TASK_PICKED | PICKED_WRONG_TASK))
set_sched_state(PICKED_WRONG_TASK);
else
set_sched_state(WILL_SCHEDULE);
} else
/* Litmus tasks should never be subject to a remote
* set_tsk_need_resched(). */
BUG_ON(is_realtime(tsk));
TRACE_TASK(tsk, "set_tsk_need_resched() ret:%p\n",
__builtin_return_address(0));
}
/* Called by the IPI handler after another CPU called smp_send_resched(). */
void sched_state_ipi(void)
{
/* If the IPI was slow, we might be in any state right now. The IPI is
* only meaningful if we are in SHOULD_SCHEDULE. */
if (is_in_sched_state(SHOULD_SCHEDULE)) {
/* Cause scheduler to be invoked.
* This will cause a transition to WILL_SCHEDULE. */
set_tsk_need_resched(current);
TRACE_STATE("IPI -> set_tsk_need_resched(%s/%d)\n",
current->comm, current->pid);
} else {
/* ignore */
TRACE_STATE("ignoring IPI in state %x (%s)\n",
get_sched_state(),
sched_state_name(get_sched_state()));
}
}
/* Called by plugins to cause a CPU to reschedule. IMPORTANT: the caller must
* hold the lock that is used to serialize scheduling decisions. */
void litmus_reschedule(int cpu)
{
int picked_transition_ok = 0;
int scheduled_transition_ok = 0;
/* The (remote) CPU could be in any state. */
/* The critical states are TASK_PICKED and TASK_SCHEDULED, as the CPU
* is not aware of the need to reschedule at this point. */
/* is a context switch in progress? */
if (cpu_is_in_sched_state(cpu, TASK_PICKED))
picked_transition_ok = sched_state_transition_on(
cpu, TASK_PICKED, PICKED_WRONG_TASK);
if (!picked_transition_ok &&
cpu_is_in_sched_state(cpu, TASK_SCHEDULED)) {
/* We either raced with the end of the context switch, or the
* CPU was in TASK_SCHEDULED anyway. */
scheduled_transition_ok = sched_state_transition_on(
cpu, TASK_SCHEDULED, SHOULD_SCHEDULE);
}
/* If the CPU was in state TASK_SCHEDULED, then we need to cause the
* scheduler to be invoked. */
if (scheduled_transition_ok) {
if (smp_processor_id() == cpu)
set_tsk_need_resched(current);
else
smp_send_reschedule(cpu);
}
TRACE_STATE("%s picked-ok:%d sched-ok:%d\n",
__FUNCTION__,
picked_transition_ok,
scheduled_transition_ok);
}
void litmus_reschedule_local(void)
{
if (is_in_sched_state(TASK_PICKED))
set_sched_state(PICKED_WRONG_TASK);
else if (is_in_sched_state(TASK_SCHEDULED | SHOULD_SCHEDULE)) {
set_sched_state(WILL_SCHEDULE);
set_tsk_need_resched(current);
}
}
#ifdef CONFIG_DEBUG_KERNEL
void sched_state_plugin_check(void)
{
if (!is_in_sched_state(TASK_PICKED | PICKED_WRONG_TASK)) {
TRACE("!!!! plugin did not call sched_state_task_picked()!"
"Calling sched_state_task_picked() is mandatory---fix this.\n");
set_sched_state(TASK_PICKED);
}
}
#define NAME_CHECK(x) case x: return #x
const char* sched_state_name(int s)
{
switch (s) {
NAME_CHECK(TASK_SCHEDULED);
NAME_CHECK(SHOULD_SCHEDULE);
NAME_CHECK(WILL_SCHEDULE);
NAME_CHECK(TASK_PICKED);
NAME_CHECK(PICKED_WRONG_TASK);
default:
return "UNKNOWN";
};
}
#endif
