lkml.org 
[lkml]   [2012]   [Nov]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 8/8] x86, cleanups: Simplify sync_core() in the case of no CPUID
On Wed, Nov 28, 2012 at 11:50:30AM -0800, H. Peter Anvin wrote:
> From: "H. Peter Anvin" <hpa@linux.intel.com>
>
> Simplify the implementation of sync_core() for the case where we may
> not have the CPUID instruction available.
>
> Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
> ---
> arch/x86/include/asm/processor.h | 27 +++++++++++++++++----------
> 1 file changed, 17 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index 9a4ee46..b381df7 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -673,17 +673,24 @@ static inline void sync_core(void)
> int tmp;
>
> #ifdef CONFIG_M486
> - if (boot_cpu_data.x86 < 5)
> - /* There is no speculative execution.
> - * jmp is a barrier to prefetching. */
> - asm volatile("jmp 1f\n1:\n" ::: "memory");
> - else
> + /*
> + * Do a CPUID if available, otherwise do a jump. The jump
> + * can conveniently enough be the jump around CPUID.
> + */
> + asm volatile("cmpl %2,%1\n\t"
> + "jl 1f\n\t"
> + "cpuid\n"
> + "1:"
> + : "=a" (tmp)
> + : "rm" (boot_cpu_data.cpuid_level), "ri" (0), "0" (1)
> + : "ebx", "ecx", "edx", "memory");
> +#else
> + /* cpuid is a barrier to speculative execution.
> + * Prefetched instructions are automatically
> + * invalidated when modified. */

While at it, you could correct this comment to adhere to kernel coding
style:

/*
* cpuid is a barrier...
* ...
*/

> + asm volatile("cpuid" : "=a" (tmp) : "0" (1)
> + : "ebx", "ecx", "edx", "memory");

... and then write this in its shorter form:

tmp = cpuid_eax(1);

to have it a bit easier on the eyes.

Thanks.

--
Regards/Gruss,
Boris.


\
 
 \ /
  Last update: 2012-11-28 22:21    [W:0.135 / U:0.408 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site