linux-kernel - Re: [PATCH 10/11] x86: Remove unnecessary ifdefs from i387 code.

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Message-ID: <4C7B454A.7050101@kernel.org>
Date:	Mon, 30 Aug 2010 08:44:42 +0300
From:	Pekka Enberg <penberg@...nel.org>
To:	Brian Gerst <brgerst@...il.com>
CC:	hpa@...or.com, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/11] x86: Remove unnecessary ifdefs from i387 code.

  Hi Brian,

On 8/30/10 2:38 AM, Brian Gerst wrote:
> On Sun, Aug 29, 2010 at 3:00 PM, Pekka Enberg<penberg@...nel.org>  wrote:
>> On Sat, Aug 28, 2010 at 7:04 PM, Brian Gerst<brgerst@...il.com>  wrote:
>>> Remove ifdefs for code that the compiler can optimize away on 64-bit.
>>>
>>> Signed-off-by: Brian Gerst<brgerst@...il.com>
>>> @@ -74,10 +74,8 @@ static void __cpuinit init_thread_xstate(void)
>>>
>>>         if (cpu_has_fxsr)
>>>                 xstate_size = sizeof(struct i387_fxsave_struct);
>>> -#ifdef CONFIG_X86_32
>>>         else
>>>                 xstate_size = sizeof(struct i387_fsave_struct);
>>> -#endif
>>>   }
>> I guess this is OK but keep in mind that cpu_has_fsxr is _not_
>> optimized by the compiler on 64-bit so the change probably increases
>> kernel text by few bytes.
> FXSR is a required feature on 64-bit, therefore cpu_has_fxsr is always true.
Yes, I realize that but it will still read boot_cpu_data at runtime, no?

             Pekka
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