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Date: Mon, 22 Apr 2024 13:17:44 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Xuewen Yan <xuewen.yan94@gmail.com>
Cc: Xuewen Yan <xuewen.yan@unisoc.com>, mingo@redhat.com,
	juri.lelli@redhat.com, vincent.guittot@linaro.org,
	dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com,
	mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com,
	yu.c.chen@intel.com, ke.wang@unisoc.com, di.shen@unisoc.com,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] sched/eevdf: Prevent vlag from going out of bounds
 when reweight_eevdf
Message-ID: <20240422111744.GO30852@noisy.programming.kicks-ass.net>
References: <20240422082238.5784-1-xuewen.yan@unisoc.com>
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On Mon, Apr 22, 2024 at 07:07:25PM +0800, Xuewen Yan wrote:
> On Mon, Apr 22, 2024 at 5:42 PM Peter Zijlstra <peterz@infradead.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()?

I think that's the wrong place. Note how __setscheduler_params() already
has set_load_weight(). And all other callers of ->prio_changed() already
seem to do set_load_weight() as well.

But that idle policy thing there still looks wrong, that sets the weight
very low but doesn't re-adjust anything.