linux-kernel - Re: [PATCH tip/core/rcu 24/24] rcu: Conditionally compile RCU's eqs warnings

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Message-ID: <20150629205528.GQ3717@linux.vnet.ibm.com>
Date:	Mon, 29 Jun 2015 13:55:28 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>, laijs@...fujitsu.com,
	dipankar@...ibm.com, Andrew Morton <akpm@...ux-foundation.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Josh Triplett <josh@...htriplett.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	David Howells <dhowells@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Darren Hart <dvhart@...ux.intel.com>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Oleg Nesterov <oleg@...hat.com>,
	pranith kumar <bobby.prani@...il.com>
Subject: Re: [PATCH tip/core/rcu 24/24] rcu: Conditionally compile RCU's eqs
 warnings

On Mon, Jun 29, 2015 at 11:39:13AM +0200, Geert Uytterhoeven wrote:
> Hi Paul,
> 
> On Wed, May 13, 2015 at 12:30 AM, Paul E. McKenney
> <paulmck@...ux.vnet.ibm.com> wrote:
> > --- a/lib/Kconfig.debug
> > +++ b/lib/Kconfig.debug
> > @@ -1373,6 +1373,17 @@ config RCU_TRACE
> >           Say Y here if you want to enable RCU tracing
> >           Say N if you are unsure.
> >
> > +config RCU_EQS_DEBUG
> > +       bool "Use this when adding any sort of NO_HZ support to your arch"
> 
> This sounds a bit fuzzy. Can you please provide a better one-line description?
> Thanks!

So the point of this Kconfig option is to provide WARN_ON()s that catch
bug such as telling RCU that a given CPU entered idle, but failing to
tell RCU when that CPU later leaves idle.  So how about this?

+       bool "Provide debugging asserts for adding NO_HZ support to an arch"

							Thanx, Paul

> > +       depends on DEBUG_KERNEL
> > +       help
> > +         This option provides consistency checks in RCU's handling of
> > +         NO_HZ.  These checks have proven quite helpful in detecting
> > +         bugs in arch-specific NO_HZ code.
> > +
> > +         Say N here if you need ultimate kernel/user switch latencies
> > +         Say Y if you are unsure
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds
> 

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