linux-kernel - Re: [PATCH v9 3/5] qrwlock, x86 - Treat all data type not bigger than long as atomic in x86

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Date:	Tue, 21 Jan 2014 16:39:58 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Waiman Long <waiman.long@...com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>,
	linux-arch@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michel Lespinasse <walken@...gle.com>,
	Andi Kleen <andi@...stfloor.org>,
	Rik van Riel <riel@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	George Spelvin <linux@...izon.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>, aswin@...com,
	Scott J Norton <scott.norton@...com>
Subject: Re: [PATCH v9 3/5] qrwlock, x86 - Treat all data type not bigger
 than long as atomic in x86

On Tue, Jan 21, 2014 at 10:36:48AM -0500, Waiman Long wrote:
> On 01/20/2014 10:03 AM, Peter Zijlstra wrote:
> >On Tue, Jan 14, 2014 at 11:44:05PM -0500, Waiman Long wrote:
> >>The generic __native_word() macro defined in include/linux/compiler.h
> >>only allows "int" and "long" data types to be treated as native and
> >>atomic. The x86 architecture, however, allow the use of char and short
> >>data types as atomic as well.
> >>
> >>This patch extends the data type allowed in the __native_word() macro to
> >>allow the use of char and short.
> >>
> >>Signed-off-by: Waiman Long<Waiman.Long@...com>
> >>---
> >>  arch/x86/include/asm/barrier.h |    8 ++++++++
> >>  1 files changed, 8 insertions(+), 0 deletions(-)
> >>
> >>diff --git a/arch/x86/include/asm/barrier.h b/arch/x86/include/asm/barrier.h
> >>index 04a4890..4d3e30a 100644
> >>--- a/arch/x86/include/asm/barrier.h
> >>+++ b/arch/x86/include/asm/barrier.h
> >>@@ -24,6 +24,14 @@
> >>  #define wmb()	asm volatile("sfence" ::: "memory")
> >>  #endif
> >>
> >>+/*
> >>+ * All data types<= long are atomic in x86
> >>+ */
> >>+#ifdef __native_word
> >>+#undef __native_word
> >>+#endif
> >>+#define __native_word(t)	(sizeof(t)<= sizeof(long))
> >Yeah, not going to happen.
> 
> Does explicit list of acceptable sizes work for you?
> 
> #define __native_word(t) (sizeof(t) == sizeof(char) || sizeof(t) ==
> sizeof(short) || sizeof(t) == sizeof(int ) ||
>                  sizeof(t) == sizeof(long))

No, generic primitives should not have arch specific behaviour.
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