Peter Zijlstra <peterz@infradead.org> 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@oracle.com>
>> ---
>> 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