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

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Message-ID: <20150317180014.GC4141@cloud>
Date:	Tue, 17 Mar 2015 11:00:14 -0700
From:	josh@...htriplett.org
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	linux-kernel@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	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 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.

> --- 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.

- Josh Triplett
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