linux-kernel - Re: [RFC PATCH v13] sys_membarrier(): system/process-wide memory barrier (x86)

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Message-ID: <20150318144147.GA5312@linux.vnet.ibm.com>
Date:	Wed, 18 Mar 2015 07:41:48 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	josh@...htriplett.org, linux-kernel@...r.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Nicholas Miell <nmiell@...cast.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Alan Cox <gnomes@...rguk.ukuu.org.uk>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Stephen Hemminger <stephen@...workplumber.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	David Howells <dhowells@...hat.com>
Subject: Re: [RFC PATCH v13] sys_membarrier(): system/process-wide memory
 barrier (x86)

On Tue, Mar 17, 2015 at 07:27:15PM +0000, Mathieu Desnoyers wrote:
> ----- Original Message -----
> > ----- Original Message -----
> > > On Tue, Mar 17, 2015 at 01:22:02PM -0400, Mathieu Desnoyers wrote:
> > > > --- a/init/Kconfig
> > > > +++ b/init/Kconfig
> > > > @@ -1568,6 +1568,15 @@ config PCI_QUIRKS
> > > >  	  bugs/quirks. Disable this only if your target machine is
> > > >  	  unaffected by PCI quirks.
> > > >  
> > > > +config MEMBARRIER
> > > > +	bool "Enable membarrier() system call" if EXPERT
> > > > +	default y
> > > > +	help
> > > > +	  Enable the membarrier() system call that allows issuing
> > > > +	  memory barriers across cores.
> > > 
> > > Nit: CPUs, not cores.  Nothing here is specific to
> > > packages/cores/threads.
> > 
> > Fixed.
> > 
> > > 
> > > > --- a/kernel/rcu/update.c
> > > > +++ b/kernel/rcu/update.c
> > > > @@ -49,6 +49,8 @@
> > > >  #include <linux/module.h>
> > > >  #include <linux/kthread.h>
> > > >  #include <linux/tick.h>
> > > > +#include <linux/syscalls.h>
> > > > +#include <linux/membarrier.h>
> > > >  
> > > >  #define CREATE_TRACE_POINTS
> > > >  
> > > > @@ -775,3 +777,73 @@ late_initcall(rcu_verify_early_boot_tests);
> > > >  #else
> > > >  void rcu_early_boot_tests(void) {}
> > > >  #endif /* CONFIG_PROVE_RCU */
> > > > +
> > > > +#ifdef CONFIG_MEMBARRIER
> > > 
> > > As mentioned in my previous mail, please consider moving this to its own
> > > file, if it doesn't use any of the internals of kernel/rcu/update.c
> > > (which I don't think it does).  That then means you can enable/disable
> > > the entire file in the Makefile rather than using an #ifdef in the .c
> > > file.
> > 
> > Will do, thanks!
> 
> I'm adding include/uapi/linux/membarrier.h and kernel/membarrier.c,
> how should I add them to the MAINTAINERS file ?

I suggest adding them as their own entry, with yourself as maintainer.
I would be willing to be co-maintainer, and perhaps some of the others
in this thread would also be willing.

							Thanx, Paul

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