A lockfree approach to check_task_state
This treates the state as an indicator variable and use it to probe
saved_state lock free. There is actually no consistency demand on
state/saved_state but rather a consistency demand on the transitions
of the two variables but those transition, based on path inspection,
are not independent.
Its probably not faster than the lock/unlock case if uncontended - atleast
it does not show up in benchmark results, but it would never be hit by a
full pi-boost cycle as there is no contention.
This also was tested against the test-case from Sebastian as well as
rnning a few scripted gdb breakpoint debugging/single-stepping loops
to trigger this.
Tested-by: Andreas Platschek <platschek@xxxxxxxxxxxxxxxx>
Tested-by: Carsten Emde <C.Emde@xxxxxxxxx>
Signed-off-by: Nicholas Mc Guire <der.herr@xxxxxxx>
---
kernel/sched/core.c | 10 ++++++++--
1 files changed, 8 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index bf93f63..5690ba3 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1074,11 +1074,17 @@ static int migration_cpu_stop(void *data);
static bool check_task_state(struct task_struct *p, long match_state)
{
bool match = false;
+ long state, saved_state;
+
+ /* catch restored state */
+ do {
+ state = p->state;
+ saved_state = p->saved_state;
+ rmb(); /* make sure we actually catch updates */
+ } while (state != p->state);
- raw_spin_lock_irq(&p->pi_lock);
if (p->state == match_state || p->saved_state == match_state)
match = true;
- raw_spin_unlock_irq(&p->pi_lock);
return match;
}
--
1.7.2.5
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