linux-kernel - Re: [PATCH 6/7] sched/rt: make it configurable

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Date:   Tue, 30 May 2017 14:31:56 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Nicolas Pitre <nicolas.pitre@...aro.org>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 6/7] sched/rt: make it configurable

On Tue, May 30, 2017 at 08:17:00AM -0400, Nicolas Pitre wrote:
> On Tue, 30 May 2017, Peter Zijlstra wrote:
> 
> > On Mon, May 29, 2017 at 05:03:01PM -0400, Nicolas Pitre wrote:
> > 
> > > @@ -1303,8 +1303,17 @@ config SCHED_AUTOGROUP
> > >  	  desktop applications.  Task group autogeneration is currently based
> > >  	  upon task session.
> > >  
> > > +config SCHED_RT
> > > +	bool "Real Time Task Scheduling" if EXPERT
> > > +	default y
> > > +	help
> > > +	  This adds the sched_rt scheduling class to the kernel providing
> > > + 	  support for the SCHED_FIFO and SCHED_RR policies. You might want
> > > +	  to disable this to reduce the kernel size. If unsure say y.
> > > +
> > >  config SCHED_DL
> > >  	bool "Deadline Task Scheduling" if EXPERT
> > > +	depends on SCHED_RT
> > >  	default y
> > >  	help
> > >  	  This adds the sched_dl scheduling class to the kernel providing
> > > @@ -1632,6 +1641,7 @@ config BASE_FULL
> > >  config FUTEX
> > >  	bool "Enable futex support" if EXPERT
> > >  	default y
> > > +	depends on SCHED_RT
> > >  	select RT_MUTEXES
> > >  	help
> > >  	  Disabling this option will cause the kernel to be built without
> > 
> > Aside from all the other completely non-starter #ifdeffery trainwrecks,
> > this is just plain wrong.
> 
> Care to elaborate?

SCHED_DL does not in any way depend on SCHED_RT and futexes should not
wholly get axed when we lack SCHED_RT.

> You might not like the approach, but you can't dismiss the goal just 
> like that. So please help me do it right.

Why can't I dismiss it? All I see is ugly that makes maintenance worse
for very little to no benefit.