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
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.
* 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);