Catalin Marinas <catalin.marinas@xxxxxxx> writes:
> On Wed, Sep 10, 2025 at 08:46:50PM -0700, Ankur Arora wrote:
>> This series adds waited variants of the smp_cond_load() primitives:
>> smp_cond_load_relaxed_timeout(), and smp_cond_load_acquire_timeout().
>>
>> As the name suggests, the new interfaces are meant for contexts where
>> you want to wait on a condition variable for a finite duration. This
>> is easy enough to do with a loop around cpu_relax() and a periodic
>> timeout check (pretty much what we do in poll_idle(). However, some
>> architectures (ex. arm64) also allow waiting on a cacheline. So,
>>
>> smp_cond_load_relaxed_timeout(ptr, cond_expr, time_check_expr)
>> smp_cond_load_acquire_timeout(ptr, cond_expr, time_check_expr)
>>
>> do a mixture of spin/wait with a smp_cond_load() thrown in.
>>
>> The added parameter, time_check_expr, determines the bail out condition.
>>
>> There are two current users for these interfaces. poll_idle() with
>> the change:
>>
>> poll_idle() {
>> ...
>> time_end = local_clock_noinstr() + cpuidle_poll_time(drv, dev);
>>
>> raw_local_irq_enable();
>> if (!current_set_polling_and_test())
>> flags = smp_cond_load_relaxed_timeout(¤t_thread_info()->flags,
>> (VAL & _TIF_NEED_RESCHED),
>> ((local_clock_noinstr() >= time_end)));
>> dev->poll_time_limit = !(flags & _TIF_NEED_RESCHED);
>> raw_local_irq_disable();
>> ...
>> }
>
> You should have added this as a patch in the series than include the
> implementation in the cover letter.
This was probably an overkill but I wanted to not add another subsystem
to this series.
Will take care of the cpuidle changes in the arm64 polling in idle series.
--
ankur
