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

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Message-ID: <20240422094157.GA34453@noisy.programming.kicks-ass.net>
Date: Mon, 22 Apr 2024 11:41:57 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Xuewen Yan <xuewen.yan94@...il.com>
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 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
set_load_weight() I'm suspicious of the task_has_idle_policy() case.