Re: [PATCH v2] sched/eevdf: Prevent vlag from going out of bounds when reweight_eevdf

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
Date: Mon, 22 Apr 2024 13:17:44 +0200	[thread overview]
Message-ID: <20240422111744.GO30852@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <CAB8ipk9M1wLXV7MWMBYGMhKbY71QqwkvchiENeWTg7JERe6kZw@mail.gmail.com>

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.