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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Message-ID: <52DE9BB0.5070909@hp.com>
Date:	Tue, 21 Jan 2014 11:09:20 -0500
From:	Waiman Long <waiman.long@...com>
To:	Peter Zijlstra <peterz@...radead.org>
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 01/21/2014 10:39 AM, Peter Zijlstra wrote:
> 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.

OK, will something like the following acceptable to you:

arch/x86/include/asm/barrier.h:

#define __arch_native_word(t) (sizeof(t) == sizeof(char) || sizeof(t) ==
sizeof(short) || sizeof(t) == sizeof(int ) ||
                  sizeof(t) == sizeof(long))

include/linux/compiler.h:

#ifndef __native_word
# ifdef __arch_native_word(t)
#  define __native_word(t)	__arch_native_word(t)
# else
#  define __native_word(t) (sizeof(t) == sizeof(int) || sizeof(t) == sizeof(long))
# endif
#endif

-Longman




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