Re: [Question] Sched: Severe scheduling latency (>10s) observed on kernel 6.12 with specific workload

[Dietmar Eggemann <dietmar.eggemann@arm.com>]

On 01.04.26 12:48, Xuewen Yan wrote:
> On Wed, Apr 1, 2026 at 6:05 PM Vincent Guittot
> <vincent.guittot@linaro.org> wrote:
>>
>> On Wed, 1 Apr 2026 at 08:04, Xuewen Yan <xuewen.yan94@gmail.com> wrote:
>>>
>>> On Wed, Apr 1, 2026 at 12:25 PM John Stultz <jstultz@google.com> wrote:
>>>>
>>>> On Tue, Mar 31, 2026 at 7:32 PM Xuewen Yan <xuewen.yan94@gmail.com> wrote:
>>>>>
>>>>> Dear Linux maintainers and reviewers,
>>>>>
>>>>> I am writing to report a severe scheduling latency issue we recently
>>>>> discovered on Linux Kernel 6.12.
>>>>>
>>>>> Issue Description
>>>>>
>>>>> We observed that when running a specific background workload pattern,
>>>>> certain tasks experience excessive scheduling latency. The delay from
>>>>> the runnable state to running on the CPU exceeds 10 seconds, and in
>>>>> extreme cases, it reaches up to 100 seconds.
>>>>>
>>>>> Environment Details
>>>>>
>>>>> Kernel Version: 6.12.58-android16-6-g3835fd28159d-ab000018-4k
>>>>> Architecture: [ ARM64]
>>>>> Hardware: T7300

Is this 4 big & 4 little CPUs?

>>>>> Config: gki_defconfig
>>>>>
>>>>> RT-app‘s workload Pattern:
>>>>>
>>>>> {
>>>>>     "tasks" : {
>>>>>             "t0" : {
>>>>>                     "instance" : 40,
>>>>>                     "priority" : 0,
>>>>>                     "cpus" : [ 0, 1, 2, 3 ],
>>>>> "taskgroup" : "/background",
>>>>>                     "loop" : -1,
>>>>>                     "run" : 200,
>>>>>                     "sleep" : 50
>>>>>             }
>>>>>     }
>>>>> }
>>>>>
>>>>> And we have applied the following patchs:
>>>>>
>>>>> https://lore.kernel.org/all/20251216111321.966709786@linuxfoundation.org/
>>>>> https://lore.kernel.org/all/20260106170509.413636243@linuxfoundation.org/
>>>>> https://lore.kernel.org/all/20260323134533.805879358@linuxfoundation.org/

Does the issue happen on v6.12.58 plain (android) or only when those 3
additional patches are applied on top?

d5843e1530d8 - sched/fair: Forfeit vruntime on yield (2025-12-18 Fernand
Sieber) v6.12.63

bddd95054e33 - sched/eevdf: Fix min_vruntime vs avg_vruntime (2026-01-08
Peter Zijlstra) v6.12.64

d2fc2dcfce47 - sched/fair: Fix zero_vruntime tracking (2026-03-25 Peter
Zijlstra) v6.12.78

[...]