linux-kernel - Re: [PATCH v4 2/2] sched: Skip priority checks with SCHED_FLAG_KEEP

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Message-ID: <cb6aaa1d-0bf4-eebc-5ffc-c1e7971564a8@arm.com>
Date:   Thu, 29 Jul 2021 19:34:14 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Quentin Perret <qperret@...gle.com>
Cc:     mingo@...hat.com, peterz@...radead.org, vincent.guittot@...aro.org,
        qais.yousef@....com, rickyiu@...gle.com, wvw@...gle.com,
        patrick.bellasi@...bug.net, xuewen.yan94@...il.com,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v4 2/2] sched: Skip priority checks with
 SCHED_FLAG_KEEP_PARAMS

On 27/07/2021 12:16, Quentin Perret wrote:
> On Monday 26 Jul 2021 at 14:56:10 (+0100), Quentin Perret wrote:
>> On Thursday 22 Jul 2021 at 10:47:33 (+0200), Dietmar Eggemann wrote:
>>> (*) This changes the behaviour when setting uclamp values on a DL task.
>>>
>>> Before uclamp values could be set but now, because of
>>>
>>>   void __getparam_dl(struct task_struct *p, struct sched_attr *attr)
>>>     ..
>>>     attr->sched_flags = dl_se->flags
>>>
>>> SCHED_FLAG_UTIL_CLAMP gets overwritten and  __sched_setscheduler() bails in:
>>>
>>>     if (unlikely(policy == p->policy)) {
>>>       ...
>>>       retval = 0;
>>>       goto unlock;
>>>     }
>>>   change:
>>>
>>> I.e. the:
>>>
>>>       if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)
>>>         goto change;
>>>
>>> can't trigger anymore.
>>
>> Bah, as you said it doesn't seem to be a big deal, but clearly that was
>> unintentional. Let me try and fix this.
> 
> While looking at this I found existing bugs in the area. Fixes are here:
> 
> https://lore.kernel.org/lkml/20210727101103.2729607-1-qperret@google.com/
> 
> And with the above series applied this patch should behave correctly
> now.

It does. Like depicted in

https://lkml.kernel.org/r/e6d103f1-f8ee-cad9-c7c0-c9ea5d0f099a@arm.com

Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>