linux-kernel - Re: [GIT PULL] x86/vdso changes for v3.16

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Date:	Fri, 6 Jun 2014 14:44:51 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	Stefani Seibold <stefani@...bold.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Pavel Emelyanov <xemul@...allels.com>
Subject: Re: [GIT PULL] x86/vdso changes for v3.16

On Fri, Jun 6, 2014 at 2:42 PM, H. Peter Anvin <hpa@...or.com> wrote:
> On 06/06/2014 02:39 PM, Andy Lutomirski wrote:
>>>
>>> For accessing memory members doing it via a pointer is pretty much TRT,
>>> but for things that might be in register it is undesirable to force it
>>> out to memory.
>>
>> Do you also believe in the folklore that GCC can optimize code
>> sequences like the things in that header?  Because I'm pretty sure
>> that no clang or gcc version I've ever seen can do it.
>>
>
> I have seen gcc do some pretty sophisticated memory elision lately.
> Don't know if that includes byte swaps.
>
>> On the other hand, even a factor of ten in the time it takes to run
>> vdso2c is completely irrelevant.
>
> Yep, as I noted in the patch I sent (which is broken - updated one
> included here.)

Acked-by: Andy Lutomirski <luto@...capital.net>

The generated vdso-image-*.c files are identical.

--Andy

>
>         -hpa
>



-- 
Andy Lutomirski
AMA Capital Management, LLC
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