Re: 50 Watt idle power regression bisected to Linux-3.10

[H. Peter Anvin]

On 12/11/2013 08:25 PM, Mike Galbraith wrote:
>  arch/x86/include/asm/mwait.h   |    4 ++--
>  arch/x86/kernel/cpu/common.c   |    7 ++++---
>  arch/x86/kernel/setup_percpu.c |    1 +
>  3 files changed, 7 insertions(+), 5 deletions(-)
> 
> Index: linux-2.6/arch/x86/kernel/cpu/common.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/kernel/cpu/common.c
> +++ linux-2.6/arch/x86/kernel/cpu/common.c
> @@ -65,13 +65,14 @@ void __init setup_cpu_local_masks(void)
>  }
>  
>  /* allocate percpu area for mwait doorbell */
> -char __percpu *mwait_doorbell;
> +DEFINE_PER_CPU(char *, mwait_doorbell);
> +EXPORT_PER_CPU_SYMBOL(mwait_doorbell);
>  

Sorry, this is wrong.  This is NOT a percpu variable, it is a pointer to
a percpu allocation, but the variable itself is not a percpu variable.
This explains your boom.

>  void __init setup_mwait_doorbell(void)
>  {
>  	if (boot_cpu_has(X86_FEATURE_MWAIT)) {
> -		mwait_doorbell = __alloc_percpu(boot_cpu_data.clflush_size,
> -						boot_cpu_data.clflush_size);
> +		mwait_doorbell = __alloc_percpu(boot_cpu_data.x86_clflush_size,
> +						boot_cpu_data.x86_clflush_size);
>  
>  		if (!mwait_doorbell) {
>  			/* This should never happen... */

	-hpa


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