Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes: > 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... Yeah, it reads like it's trying to say something when it is just trying to check a bit. Does the new one read better? -- ankur
