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Message-ID: <493994B35A117E4F832F97C4719C4C040132BE85FE@orsmsx505.amr.corp.intel.com>
Date: Wed, 3 Aug 2011 09:34:46 -0700
From: "Yu, Fenghua" <fenghua.yu@...el.com>
To: Andy Lutomirski <luto@....EDU>, "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
> -----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.
>
> + 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 With your patch, the comment is out-of-date.
> */
> if (c->x86 > 6 || (c->x86 == 6 && c->x86_model >= 0xd)) {
> rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
> +
> + if (allow_fast_string &&
> + !(misc_enable & MSR_IA32_MISC_ENABLE_FAST_STRING)) {
> + misc_enable |= MSR_IA32_MISC_ENABLE_FAST_STRING;
> + wrmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
> + printk(KERN_INFO "Enabled fast string operations\n");
> +
> + /* Re-read to make sure it stuck. */
> + rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
> + }
> +
> if (!(misc_enable & MSR_IA32_MISC_ENABLE_FAST_STRING)) {
> printk(KERN_INFO "Disabled fast string
> operations\n");
> setup_clear_cpu_cap(X86_FEATURE_REP_GOOD);
> --
> 1.7.6
--
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