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Message-ID: <20181107145527.GI9761@hirez.programming.kicks-ass.net>
Date: Wed, 7 Nov 2018 15:55:27 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Patrick Bellasi <patrick.bellasi@....com>
Cc: linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
Ingo Molnar <mingo@...hat.com>, Tejun Heo <tj@...nel.org>,
"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Viresh Kumar <viresh.kumar@...aro.org>,
Paul Turner <pjt@...gle.com>,
Quentin Perret <quentin.perret@....com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Morten Rasmussen <morten.rasmussen@....com>,
Juri Lelli <juri.lelli@...hat.com>,
Todd Kjos <tkjos@...gle.com>,
Joel Fernandes <joelaf@...gle.com>,
Steve Muckle <smuckle@...gle.com>,
Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: [PATCH v5 03/15] sched/core: uclamp: map TASK's clamp values
into CPU's clamp groups
On Wed, Nov 07, 2018 at 02:48:09PM +0000, Patrick Bellasi wrote:
> On 07-Nov 14:35, Peter Zijlstra wrote:
> You mean se_count overflow ?
Yah..
> > And I'm not really a fan of hiding that error in a define like you keep
> > doing.
>
> The #define is not there to mask an overflow, it's there to catch the
+#define UCLAMP_MAPERR "clamp value [%u] mapping to clamp group failed\n"
Is what I was talking about.
> > What's wrong with something like:
> >
> > if (SCHED_WARN(free_group_id == UCLAMP_GROUPS))
> > return;
>
> Right, the flow should be:
>
> 1. try to find a valid clamp group
> 2. if you don't find one, the data structures are corrupted
> warn once for data corruption
> do not map this scheduling entity and return
> 3. map the scheduling entity
>
> Is that ok ?
That's what the proposed does.
> > and
> >
> > > + uc_map_new.se_count = uc_map_old.se_count + 1;
> >
> > if (SCHED_WARN(!new.se_count))
> > new.se_count = -1;
>
> Mmm... not sure we can recover from a corrupted refcount or an
> overflow.
>
> What should we do on these cases, disable uclamp completely ?
You can teach put to never decrement -1 (aka. all 1s).
But its all SCHED_DEBUG stuff anyway, so who really cares.
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