Re: [REGRESSION] 6.12.y: d66792919d4f (sched/deadline: Use revised wakeup rule for dl_server) causes latencies up to 50ms with PREEMPT_RT

On 5/16/26 21:50, Lukas Beckmann wrote:
> On Tue, May 12, 2026 at 12:08:49AM +0200, Lukas Beckmann wrote:
>> On 5/11/26 16:21, Sasha Levin wrote:
>>> Thanks for the detailed report. Before I revert d66792919d4f from 6.12.y,
>>> I'd like to confirm whether the underlying issue is the missing dl_server
>>> rework chain on 6.12.y rather than the revised wakeup rule itself.
>>>
>>> Mike's reply notes that his local 6.12-rt tree carrying the following
>>> three commits in cannot reproduce, while the same tree without them
>>> reproduces quickly:
>>>
>>>    cccb45d7c429 ("sched/deadline: Less agressive dl_server handling")
>>>    4ae8d9aa9f9d ("sched/deadline: Fix dl_server getting stuck")
>>>    a3a70caf7906 ("sched/deadline: Fix dl_server behaviour")
>>>
>>> d66792919d4f's upstream commit message explicitly says it relies on the
>>> state established by a3a70caf7906, and none of the three are in 6.12.y.
>>>
>>> Could you give those three commits a spin on top of 6.12.y (keeping
>>> d66792919d4f in place) and see whether the latency goes away?
>>
>> If I apply the three commits on 6.12.y, the latencies indeed go away.
>> This is running for a few hours now, and the latencies showed up after 30
>> minutes tops, with plain 6.12.y before.
>> I will leave this running.
>
> Cyclictest is still running and looking good (latency-wise).
> How should we proceed?

Sasha, just wondering: is this still in your queue? It sounds like a
clear case to pick those three up for 6.12.y (everybody: please correct
me if I'm wrong). Or are you busy and should we ask Greg to pick them up?

Ciao, Thorsten