linux-kernel - Re: [RFC PATCH 4/6] Preempt-RCU: Implementation

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 28 Feb 2008 20:53:28 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Roman Zippel <zippel@...ux-m68k.org>
Cc:	ego@...ibm.com, linux-kernel@...r.kernel.org,
	linux-rt-users@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Ted Tso <tytso@...ibm.com>, dvhltc@...ibm.com,
	Oleg Nesterov <oleg@...sign.ru>,
	Andrew Morton <akpm@...ux-foundation.org>, bunk@...nel.org,
	Josh Triplett <josh@...edesktop.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [RFC PATCH 4/6] Preempt-RCU: Implementation

On Fri, Feb 29, 2008 at 05:34:54AM +0100, Roman Zippel wrote:
> Hi,
> 
> On Thursday 13. December 2007, Gautham R Shenoy wrote:
> 
> > diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
> > index c64ce9c..06cafcc 100644
> > --- a/kernel/Kconfig.preempt
> > +++ b/kernel/Kconfig.preempt
> > @@ -63,3 +63,41 @@ config PREEMPT_BKL
> >  	  Say Y here if you are building a kernel for a desktop system.
> >  	  Say N if you are unsure.
> >
> > +choice
> > +	prompt "RCU implementation type:"
> > +	default CLASSIC_RCU
> > +
> > +config CLASSIC_RCU
> > +	bool "Classic RCU"
> > +	help
> > +	  This option selects the classic RCU implementation that is
> > +	  designed for best read-side performance on non-realtime
> > +	  systems.
> > +
> > +	  Say Y if you are unsure.
> > +
> > +config PREEMPT_RCU
> > +	bool "Preemptible RCU"
> > +	depends on PREEMPT
> > +	help
> > +	  This option reduces the latency of the kernel by making certain
> > +	  RCU sections preemptible. Normally RCU code is non-preemptible, if
> > +	  this option is selected then read-only RCU sections become
> > +	  preemptible. This helps latency, but may expose bugs due to
> > +	  now-naive assumptions about each RCU read-side critical section
> > +	  remaining on a given CPU through its execution.
> > +
> > +	  Say N if you are unsure.
> > +
> > +endchoice
> 
> Why got this moved into init/Kconfig?

Because there are some arches that don't have kernel/Kconfig.preempt,
its earlier home.  Therefore, putting it into kernel/Kconfig.preempt
broke those arches' builds by supplying neither PREEMPT_RCU nor
CLASSIC_RCU.

> Now it's somewhere in the root menu, not really belonging to anything.

Do you have a suggested location?

> Also why is this a choice? Are more RCU types planned?

I don't expect additional drop-in replacements for RCU, though people
are certainly free to experiment if they wish.  It is a choice because
this gives people a very clear idea of the two options and because
it makes the implementation a bit cleaner.

							Thanx, Paul
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/