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

Johannes Weiner
2007-12-13T22:59:58Z

Hi,

Eduard-Gabriel Munteanu <eduard.munteanu@linux360.ro> 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