Re: [PATCH] Option to disable AMD C1E (allows dynticks to work)

[Johannes Weiner]

Hi,

Eduard-Gabriel Munteanu <eduard.munteanu@xxxxxxxxxxx> writes:

> diff --git a/arch/x86/kernel/setup_64.c b/arch/x86/kernel/setup_64.c
> index 30d94d1..15556a0 100644
> --- a/arch/x86/kernel/setup_64.c
> +++ b/arch/x86/kernel/setup_64.c
> @@ -583,6 +583,17 @@ static void __init amd_detect_cmp(struct cpuinfo_x86 *c)
>  #endif
>  }
>  
> +#ifdef CONFIG_X86_AMD_C1E_WORKAROUND
> +static int __cpuinit disable_amd_c1e = 1;
> +
> +static int __cpuinit force_amd_c1e(char *str) {
> +	disable_amd_c1e = 0;
> +	return 1;
> +}
> +
> +__setup("force_amd_c1e", force_amd_c1e);
> +#endif /* CONFIG_X86_AMD_C1E_WORKAROUND */
> +
>  #define ENABLE_C1E_MASK		0x18000000
>  #define CPUID_PROCESSOR_SIGNATURE	1
>  #define CPUID_XFAM		0x0ff00000
> @@ -597,6 +608,7 @@ static __cpuinit int amd_apic_timer_broken(void)
>  {
>  	u32 lo, hi;
>  	u32 eax = cpuid_eax(CPUID_PROCESSOR_SIGNATURE);
> +
>  	switch (eax & CPUID_XFAM) {
>  	case CPUID_XFAM_K8:
>  		if ((eax & CPUID_XMOD) < CPUID_XMOD_REV_F)
> @@ -604,8 +616,19 @@ static __cpuinit int amd_apic_timer_broken(void)
>  	case CPUID_XFAM_10H:
>  	case CPUID_XFAM_11H:
>  		rdmsr(MSR_K8_ENABLE_C1E, lo, hi);
> -		if (lo & ENABLE_C1E_MASK)
> -			return 1;
> +#ifdef CONFIG_X86_AMD_C1E_WORKAROUND
> +		if ((lo & ENABLE_C1E_MASK) && disable_amd_c1e) {
> +			printk(KERN_INFO "Disabling AMD C1E on CPU %d\n",
> +			       smp_processor_id());
> +			/* 
> +			 * See AMD's "BIOS and Kernel Developer's Guide for AMD
> +			 * NPT Family 0Fh Processors", publication #32559,
> +			 * for details.
> +			 */
> +			wrmsr(MSR_K8_ENABLE_C1E, lo & ~ENABLE_C1E_MASK, hi); 
> +		} else 
> +#endif /* CONFIG_X86_AMD_C1E_WORKAROUND */
> +		if (lo & ENABLE_C1E_MASK) return 1;

I would find this way more readable:

	if (lo & ENABLE_C1E_MASK) {
#ifdef CONFIG_X86_AMD_C1E_WORKAROUND
		if (disable_amd_c1e) {
			...
#else
		return 1;
#endif
	}

Why does it require to be enabled by compile-time AND run-time?  Is that
something you might want to decide on every boot?  Could we make it
settable at boot-time xor at compile-time?

	Hannes
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