Catalin Marinas <catalin.marinas@xxxxxxx> writes:
> On Tue, Sep 02, 2025 at 03:46:52PM -0700, Ankur Arora wrote:
>> Catalin Marinas <catalin.marinas@xxxxxxx> writes:
>> > Can you have a go at poll_idle() to see how it would look like using
>> > this API? It doesn't necessarily mean we have to merge them all at once
>> > but it gives us a better idea of the suitability of the interface.
>>
>> So, I've been testing with some version of the following:
>>
>> diff --git a/drivers/cpuidle/poll_state.c b/drivers/cpuidle/poll_state.c
>> index 9b6d90a72601..361879396d0c 100644
>> --- a/drivers/cpuidle/poll_state.c
>> +++ b/drivers/cpuidle/poll_state.c
>> @@ -8,35 +8,25 @@
>> #include <linux/sched/clock.h>
>> #include <linux/sched/idle.h>
>>
>> -#define POLL_IDLE_RELAX_COUNT 200
>> -
>> static int __cpuidle poll_idle(struct cpuidle_device *dev,
>> struct cpuidle_driver *drv, int index)
>> {
>> - u64 time_start;
>> -
>> - time_start = local_clock_noinstr();
>> + unsigned long flags;
>>
>> dev->poll_time_limit = false;
>>
>> raw_local_irq_enable();
>> if (!current_set_polling_and_test()) {
>> - unsigned int loop_count = 0;
>> - u64 limit;
>> + u64 limit, time_end;
>>
>> limit = cpuidle_poll_time(drv, dev);
>> + time_end = local_clock_noinstr() + limit;
>>
>> - while (!need_resched()) {
>> - cpu_relax();
>> - if (loop_count++ < POLL_IDLE_RELAX_COUNT)
>> - continue;
>> + flags = smp_cond_load_relaxed_timewait(¤t_thread_info()->flags,
>> + VAL & _TIF_NEED_RESCHED,
>> + (local_clock_noinstr() >= time_end));
>
> It makes sense to have the non-strict comparison, though it changes the
> original behaviour slightly. Just mention it in the commit log.
>
>>
>> - loop_count = 0;
>> - if (local_clock_noinstr() - time_start > limit) {
>> - dev->poll_time_limit = true;
>> - break;
>> - }
>> - }
>> + dev->poll_time_limit = (local_clock_noinstr() >= time_end);
>
> Could we do this instead and avoid another clock read:
>
> dev->poll_time_limit = !(flags & _TIF_NEED_RESCHED);
>
> In the original code, it made sense since it had to check the clock
> anyway and break the loop.
>
> When you repost, please include the rqspinlock and poll_idle changes as
> well to show how the interface is used.
Sure.
--
ankur
