linux-kernel - Re: [PATCH v2] sched/eevdf: Prevent vlag from going out of bounds when reweight

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Message-ID: <CAB8ipk9M1wLXV7MWMBYGMhKbY71QqwkvchiENeWTg7JERe6kZw@mail.gmail.com>
Date: Mon, 22 Apr 2024 19:07:25 +0800
From: Xuewen Yan <xuewen.yan94@...il.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Xuewen Yan <xuewen.yan@...soc.com>, mingo@...hat.com, juri.lelli@...hat.com, 
	vincent.guittot@...aro.org, dietmar.eggemann@....com, rostedt@...dmis.org, 
	bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com, 
	yu.c.chen@...el.com, ke.wang@...soc.com, di.shen@...soc.com, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sched/eevdf: Prevent vlag from going out of bounds
 when reweight_eevdf

On Mon, Apr 22, 2024 at 5:42 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Mon, Apr 22, 2024 at 04:33:37PM +0800, Xuewen Yan wrote:
>
> > On the Android system, the nice value of a task will change very
> > frequently. The limit can also be exceeded.
> > Maybe the !on_rq case is still necessary.
> > So I'm planning to propose another patch for !on_rq case later after
> > careful testing locally.
>
> So the scaling is: vlag = vlag * old_Weight / weight
>
> But given that integer devision is truncating, you could expect repeated
> application of such scaling would eventually decrease the vlag instead
> of grow it.
>
> Is there perhaps an invocation of reweight_task() missing? Looking at

Is it necessary to add reweight_task in the prio_changed_fair()?

> set_load_weight() I'm suspicious of the task_has_idle_policy() case.