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 <[email protected]> Tested-by: Carsten Emde <[email protected]> Signed-off-by: Nicholas Mc Guire <[email protected]> --- 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
