linux-kernel - Re: [PATCH v5 1/1] sched/uclamp: add SCHED_FLAG_UTIL_CLAMP

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Date:   Thu, 12 Nov 2020 17:01:46 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Qais Yousef <qais.yousef@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Yun Hsiang <hsiang023167@...il.com>,
        linux-kernel@...r.kernel.org, patrick.bellasi@...bug.net,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v5 1/1] sched/uclamp: add SCHED_FLAG_UTIL_CLAMP_RESET flag
 to reset uclamp

On 12/11/2020 15:41, Qais Yousef wrote:
> On 11/11/20 18:41, Dietmar Eggemann wrote:
>> On 10/11/2020 13:21, Peter Zijlstra wrote:
>>> On Tue, Nov 03, 2020 at 10:37:56AM +0800, Yun Hsiang wrote:

[...]

> I assume we agree then that we don't want to explicitly document this quirky
> feature and keep it for advanced users?
> 
> I am wary of the UAPI change that is both explicit and implicit. It explicitly
> requests a reset, but implicitly requests a cgroup behavior change.
> 
> With this magic value at least we can more easily return an error if we decided
> to deprecate it, which has been my main ask so far. I don't want us to end up
> not being able to easily modify this code in the future.

Another advantage for this 'magic value' approach.

> I don't have strong opinion too though.
> 
> If you or Yun would still like to send the patch to protect
> SCHED_FLAG_UTIL_CLAMP and SCHED_FLAG_ALL with __kernel__ that'd be great.

Ah yes! Can add an extra patch for this when sending out the next version.

[...]