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sched: Cache task_struct::flags in sched_submit_work()

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sched_submit_work() is considered to be a hot path. The preempt_disable()
instruction is a compiler barrier and forces the compiler to load
task_struct::flags for the second comparison.
By using a local variable, the compiler can load the value once and keep it in
a register for the second comparison.

Verified on x86-64 with gcc-10.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200819200025.lqvmyefqnbok5i4f@linutronix.de
This commit is contained in:
Sebastian Andrzej Siewior 2020-08-19 22:00:25 +02:00 committed by Peter Zijlstra
parent 01ccf59236
commit c1cecf884a
1 changed files with 5 additions and 2 deletions
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7
kernel/sched/core.c
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@ -4551,9 +4551,12 @@ void __noreturn do_task_dead(void)
static inline void sched_submit_work(struct task_struct *tsk)
{
unsigned int task_flags;
if (!tsk->state)
return;
task_flags = tsk->flags;
/*
* If a worker went to sleep, notify and ask workqueue whether
* it wants to wake up a task to maintain concurrency.
@ -4562,9 +4565,9 @@ 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 (task_flags & (PF_WQ_WORKER | PF_IO_WORKER)) {
preempt_disable();
if (tsk->flags & PF_WQ_WORKER)
if (task_flags & PF_WQ_WORKER)
wq_worker_sleeping(tsk);
else
io_wq_worker_sleeping(tsk);