linux-kernel - Re: [PATCH 1/2] x86: Enable fast strings on Intel if BIOS hasn't already

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Date:	Wed, 3 Aug 2011 12:39:49 -0400
From:	Andrew Lutomirski <luto@....edu>
To:	"Yu, Fenghua" <fenghua.yu@...el.com>
Cc:	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] x86: Enable fast strings on Intel if BIOS hasn't already

On Wed, Aug 3, 2011 at 12:34 PM, Yu, Fenghua <fenghua.yu@...el.com> wrote:
>
>
>> -----Original Message-----
>> From: Andy Lutomirski [mailto:luto@....EDU]
>> Sent: Wednesday, August 03, 2011 8:47 AM
>> To: x86@...nel.org; linux-kernel@...r.kernel.org
>> Cc: Yu, Fenghua; Andy Lutomirski
>> Subject: [PATCH 1/2] x86: Enable fast strings on Intel if BIOS hasn't
>> already
>>
>> I have two Sandy Bridge systems and neither one enables fast strings
>> in BIOS.  I can't find anything in the manual that says that only
>> BIOS should enable or disable the feature, so try to enable it at
>> bootup.
>>
>> Signed-off-by: Andy Lutomirski <luto@....edu>
>> ---
>>  arch/x86/kernel/cpu/intel.c |   17 +++++++++++++++--
>>  1 files changed, 15 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
>> index ed6086e..6b20fef 100644
>> --- a/arch/x86/kernel/cpu/intel.c
>> +++ b/arch/x86/kernel/cpu/intel.c
>> @@ -30,6 +30,7 @@
>>  static void __cpuinit early_init_intel(struct cpuinfo_x86 *c)
>>  {
>>       u64 misc_enable;
>> +     bool allow_fast_string = true;
>>
>>       /* Unmask CPUID levels if masked: */
>>       if (c->x86 > 6 || (c->x86 == 6 && c->x86_model >= 0xd)) {
>> @@ -118,10 +119,11 @@ static void __cpuinit early_init_intel(struct
>> cpuinfo_x86 *c)
>>        * (model 2) with the same problem.
>>        */
>>       if (c->x86 == 15) {
>> -             rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
>> +             allow_fast_string = false;
>> +             printk(KERN_INFO "kmemcheck: Disabling fast string
>> operations\n");
>
> Please don't move this printk() here. Keep it in the original place. If fast string bit is 0 already, we don't need to print the info.

I'll rework it.

>
>>
>> +             rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
>>               if (misc_enable & MSR_IA32_MISC_ENABLE_FAST_STRING) {
>> -                     printk(KERN_INFO "kmemcheck: Disabling fast string
>> operations\n");
>>
>>                       misc_enable &= ~MSR_IA32_MISC_ENABLE_FAST_STRING;
>>                       wrmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
>> @@ -135,6 +137,17 @@ static void __cpuinit early_init_intel(struct
>> cpuinfo_x86 *c)
>
> You also need to change the comment right before this code. With your patch, the comment is out-of-date.

Will do.

--Andy
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