After a kthread is created it signals the requester using complete() and enters TASK_UNINTERRUPTIBLE. However, since complete() wakes up the requesting thread this can cause a preemption. The preemption will not remove the task from the runqueue (for that schedule() has to be invoked directly).
This is a problem if directly after kthread creation you try to do a kthread_bind(), which will block in HZ steps until the thread is off the runqueue. This patch disables preemption during complete(), since we call schedule() directly afterwards, so it will correctly enter TASK_UNINTERRUPTIBLE. This speeds up kthread creation/binding during cpu hotplug significantly. Signed-off-by: Peter Boonstoppel <pboonstop...@nvidia.com> --- kernel/kthread.c | 11 +++++++++++ 1 files changed, 11 insertions(+), 0 deletions(-) diff --git a/kernel/kthread.c b/kernel/kthread.c index b579af5..757d8dd 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -16,6 +16,7 @@ #include <linux/mutex.h> #include <linux/slab.h> #include <linux/freezer.h> +#include <linux/preempt.h> #include <trace/events/sched.h> static DEFINE_SPINLOCK(kthread_create_lock); @@ -113,7 +114,17 @@ static int kthread(void *_create) /* OK, tell user we're spawned, wait for stop or wakeup */ __set_current_state(TASK_UNINTERRUPTIBLE); create->result = current; + + /* + * Disable preemption so we enter TASK_UNINTERRUPTIBLE after + * complete() instead of possibly being preempted. This speeds + * up clients that do a kthread_bind() directly after + * creation. + */ + preempt_disable(); complete(&create->done); + preempt_enable_no_resched(); + schedule(); ret = -EINTR; -- 1.7.0.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/