Re: [PATCH v2] cpuidle: Deny idle entry when CPU already have IPI interrupt pending

[Maulik Shah (mkshah)]

On 8/18/2026 9:40 PM, Christian Loehle wrote:
> On 4/13/26 06:03, Maulik Shah (mkshah) wrote:
>>
>>
>> On 4/6/2026 8:37 PM, Rafael J. Wysocki wrote:
>>> On Fri, Apr 3, 2026 at 6:08 AM Maulik Shah <maulik.shah@xxxxxxxxxxxxxxxx> wrote:
>>>>
>>>> CPU can get IPI interrupt from another CPU while it is executing
>>>> cpuidle_select() or about to execute same. The selection do not account
>>>> for pending interrupts and may continue to enter selected idle state only
>>>> to exit immediately.
>>>>
>>>> Example trace collected when there is cross CPU IPI.
>>>>
>>>>  [000] 154.892148: sched_waking: comm=sugov:4 pid=491 prio=-1 target_cpu=007
>>>>  [000] 154.892148: ipi_raise: target_mask=00000000,00000080 (Function call interrupts)
>>>>  [007] 154.892162: cpu_idle: state=2 cpu_id=7
>>>>  [007] 154.892208: cpu_idle: state=4294967295 cpu_id=7
>>>>  [007] 154.892211: irq_handler_entry: irq=2 name=IPI
>>>>  [007] 154.892211: ipi_entry: (Function call interrupts)
>>>>  [007] 154.892213: sched_wakeup: comm=sugov:4 pid=491 prio=-1 target_cpu=007
>>>>  [007] 154.892214: ipi_exit: (Function call interrupts)
>>>>
>>>> This impacts performance and the above count increments.
>>>>
>>>> commit ccde6525183c ("smp: Introduce a helper function to check for pending
>>>> IPIs") already introduced a helper function to check the pending IPIs and
>>>> it is used in pmdomain governor to deny the cluster level idle state when
>>>> there is a pending IPI on any of cluster CPUs.
>>>>
>>>> This however does not stop CPU to enter CPU level idle state. Make use of
>>>> same at CPUidle to deny the idle entry when there is already IPI pending.
>>>>
>>>> With change observing glmark2 [1] off screen scores improving in the range
>>>> of 25% to 30% on Qualcomm lemans-evk board which is arm64 based having two
>>>> clusters each with 4 CPUs.
>>>>
>>>> [1] https://github.com/glmark2/glmark2
>>>>
>>>> Signed-off-by: Maulik Shah <maulik.shah@xxxxxxxxxxxxxxxx>
>>>> ---
>>>> Changes in v2:
>>>> - Fix cpumask argument of cpus_peek_for_pending_ipi() to take single cpu
>>>> - Link to v1: https://lore.kernel.org/r/20260316-cpuidle_ipi-v1-1-d0ff6350f4e2@xxxxxxxxxxxxxxxx
>>>> ---
>>>>  drivers/cpuidle/cpuidle.c | 3 +++
>>>>  1 file changed, 3 insertions(+)
>>>>
>>>> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
>>>> index c7876e9e024f9076663063ad21cfc69343fdbbe7..c01e57df64ca5af8c28da3d971500b3f38306cdf 100644
>>>> --- a/drivers/cpuidle/cpuidle.c
>>>> +++ b/drivers/cpuidle/cpuidle.c
>>>> @@ -224,6 +224,9 @@ noinstr int cpuidle_enter_state(struct cpuidle_device *dev,
>>>>         bool broadcast = !!(target_state->flags & CPUIDLE_FLAG_TIMER_STOP);
>>>>         ktime_t time_start, time_end;
>>>>
>>>> +       if (cpus_peek_for_pending_ipi(cpumask_of(dev->cpu)))
>>>> +               return -EBUSY;
>>>> +
>>>
>>> Why do you want to check it here and not in cpuidle_idle_call(), for example?
>>
>> It can be moved in cpuidle_idle_call(), just before call_cpuidle() too.
>> The intention is to check after cpuidle_select() is done.
>>
> What do we do about the cpuidle stats in that case?
> I'm thinking primiarly about last_residency_ns and rejected here.

As the idle entry will not happen (call_cpuidle() is not invoked) 
the stats would also not required to be updated.

Thanks,
Maulik