On 8/19/20 6:15 AM, peterz@xxxxxxxxxxxxx wrote:
> 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?
Yes, the raw spinlock would do it, and leave the single branch intact
in the hot path. I'd be fine with going that route for io-wq.
--
Jens Axboe
