linux-kernel - Re: [RFC PATCH RT v2 1/2] time/hrtimer: Add PINNED

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Message-ID: <YNAlO4CScpaj65HG@localhost.localdomain>
Date:   Mon, 21 Jun 2021 07:35:55 +0200
From:   Juri Lelli <juri.lelli@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     bigeasy@...utronix.de, linux-rt-users@...r.kernel.org,
        peterz@...radead.org, linux-kernel@...r.kernel.org,
        bristot@...hat.com, Anna-Maria Behnsen <anna-maria@...utronix.de>
Subject: Re: [RFC PATCH RT v2 1/2] time/hrtimer: Add PINNED_HARD mode for
 realtime hrtimers

Hi,

On 19/06/21 09:56, Thomas Gleixner wrote:
> On Sat, Jun 19 2021 at 01:35, Thomas Gleixner wrote:
> > The wild west of anything which scratches 'my itch' based on 'my use
> > case numbers' in Linux ended many years ago and while RT was always a
> > valuable playground for unthinkable ideas we definitely tried hard not
> > to accept use case specific hacks wihtout a proper justification that it
> > makes sense in general.
> >
> > So why are you even trying to sell this to me?
> 
> I wouldn't have been that grumpy if you'd at least checked whether the
> task is pinned. Still I would have told you that you "fix" it at the
> wrong place.

Ah, indeed. Pulled the trigger too early it seems. I'll ponder more.

> Why on earth is that nohz heuristic trainwreck not even checking that?
> It's not a RT problem and it's not a problem restricted to RT tasks
> either. If a task is pinned then arming the timer on a random other CPU
> is blatant nonsense independent of the scheduling class.

Agree. Lemme look more into it.

Thanks for the comments!

Best,
Juri