On Wed, Aug 19, 2020 at 02:37:58PM +0200, Sebastian Andrzej Siewior wrote:
> I don't see a significant reason why this lock should become a
> raw_spinlock_t therefore I suggest to move it after the
> tsk_is_pi_blocked() check.
> Any feedback on this vs raw_spinlock_t?
>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> ---
> fs/io-wq.c | 8 ++++----
> kernel/sched/core.c | 10 +++++-----
> 2 files changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 3bbb60b97c73c..b76c0f27bd95e 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4694,18 +4694,18 @@ static inline void sched_submit_work(struct task_struct *tsk)
> * in the possible wakeup of a kworker and because wq_worker_sleeping()
> * requires it.
> */
> - if (tsk->flags & (PF_WQ_WORKER | PF_IO_WORKER)) {
> + if (tsk->flags & PF_WQ_WORKER) {
> preempt_disable();
> - if (tsk->flags & PF_WQ_WORKER)
> - wq_worker_sleeping(tsk);
> - else
> - io_wq_worker_sleeping(tsk);
> + wq_worker_sleeping(tsk);
> preempt_enable_no_resched();
> }
>
> if (tsk_is_pi_blocked(tsk))
> return;
>
> + if (tsk->flags & PF_IO_WORKER)
> + io_wq_worker_sleeping(tsk);
> +
Urgh, so this adds a branch in what is normally considered a fairly hot
path.
I'm thinking that the raw_spinlock_t option would permit leaving that
single:
if (tsk->flags & (PF_WQ_WORKER | PF_IO_WORKER))
branch intact?
