linux-kernel - Re: [PATCH] cmpxchg: Discard unnecessary cast to volatile

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Message-ID: <CAJhHMCAEEiumQVx93K069GY-XQ3RzyDOSK6-9qL9BSEc4z23YQ@mail.gmail.com>
Date:	Tue, 21 Oct 2014 18:15:58 -0400
From:	Pranith Kumar <bobby.prani@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"maintainer:X86 ARCHITECTURE..." <x86@...nel.org>,
	Borislav Petkov <bp@...e.de>,
	"open list:X86 ARCHITECTURE..." <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cmpxchg: Discard unnecessary cast to volatile

On Tue, Oct 21, 2014 at 11:48 AM, H. Peter Anvin <hpa@...or.com> wrote:
> On 10/21/2014 03:14 AM, Peter Zijlstra wrote:
>> On Mon, Oct 20, 2014 at 04:22:27PM -0400, Pranith Kumar wrote:
>>>> Generating a volatile pointer is really not necessary here. This is the only
>>>> location where a volatile pointer is being generated for use in asm.
>>>>
>>>> This commit removes the unnecessary volatile pointer being created.
>>>>
>>>> Signed-off-by: Pranith Kumar <bobby.prani@...il.com>
>>
>> Seems sane enough to me.
>>
>
> However, it seems like unnecessary churn.  Does the volatile hurt in any
> way?

Removing 4 lines of unnecessary code seems to be worthwhile to me.
Also, we reduce the unnecessary use of 'volatile' data types which
IMHO makes this a good little clean up.

I am not sure if the use of volatile actually causes any loss of
chances of optimization. I've tried to come up with cases where this
happens and was unsuccessful.

-- 
Pranith
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