On Tue, Nov 07, 2023 at 01:57:22PM -0800, Ankur Arora wrote: > The scheduling policy for RESCHED_lazy (TIF_NEED_RESCHED_LAZY) is > to let anything running in the kernel run to completion. > Accordingly, while deciding whether to call preempt_schedule_irq() > narrow the check to tif_need_resched(RESCHED_eager). > > Also add a comment about why we need to check at all, given that we > have aleady checked the preempt_count(). > > Signed-off-by: Ankur Arora <ankur.a.arora@xxxxxxxxxx> > --- > kernel/entry/common.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/kernel/entry/common.c b/kernel/entry/common.c > index 0d055c39690b..6433e6c77185 100644 > --- a/kernel/entry/common.c > +++ b/kernel/entry/common.c > @@ -384,7 +384,15 @@ void irqentry_exit_cond_resched(void) > rcu_irq_exit_check_preempt(); > if (IS_ENABLED(CONFIG_DEBUG_ENTRY)) > WARN_ON_ONCE(!on_thread_stack()); > - if (need_resched()) > + > + /* > + * If the scheduler really wants us to preempt while returning > + * to kernel, it would set TIF_NEED_RESCHED. > + * On some archs the flag gets folded in preempt_count, and > + * thus would be covered in the conditional above, but not all > + * archs do that, so check explicitly. > + */ > + if (tif_need_resched(RESCHED_eager)) > preempt_schedule_irq(); See, I'm reading this like if we're eager to preempt, but then it's not actually eager at all and only wants to preempt when forced. This naming sucks...
