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

[Xuewen Yan]

On Wed, Apr 1, 2026 at 9:00 PM Dietmar Eggemann
<dietmar.eggemann@xxxxxxx> wrote:
>
> On 01.04.26 12:48, Xuewen Yan wrote:
> > On Wed, Apr 1, 2026 at 6:05 PM Vincent Guittot
> > <vincent.guittot@xxxxxxxxxx> wrote:
> >>
> >> On Wed, 1 Apr 2026 at 08:04, Xuewen Yan <xuewen.yan94@xxxxxxxxx> wrote:
> >>>
> >>> On Wed, Apr 1, 2026 at 12:25 PM John Stultz <jstultz@xxxxxxxxxx> wrote:
> >>>>
> >>>> On Tue, Mar 31, 2026 at 7:32 PM Xuewen Yan <xuewen.yan94@xxxxxxxxx> 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?

6 little + 2big.
On our devices, background tasks are bound to cores 0-3. To mimic the
behavior of these background tasks, we also bound rt-app to cores 0-3.

>
> >>>>> 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@xxxxxxxxxxxxxxxxxxx/
> >>>>> https://lore.kernel.org/all/20260106170509.413636243@xxxxxxxxxxxxxxxxxxx/
> >>>>> https://lore.kernel.org/all/20260323134533.805879358@xxxxxxxxxxxxxxxxxxx/
>
> Does the issue happen on v6.12.58 plain (android) or only when those 3
> additional patches are applied on top?

The issue was discovered on android16-6.12.58. We applied the
following three patches, but the issue is still reproducible.

>
> 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

Thanks!