Re: [kvm-ppc-devel] [PATCH 1 of 2] Add MSR Wait state to

[Hollis Blanchard <hollisb@us.ibm.com>]

On Fri, 2008-03-28 at 16:34 -0500, Jerone Young wrote:
> # HG changeset patch
> # User Jerone Young <jyoung5@us.ibm.com>
> # Date 1206720510 18000
> # Node ID e48cf2ad6c85c457ff64c04b83960fc305420842
> # Parent  1506aa38ddabb0bf73fff3ac3f3db5f9ef6458cc
> Add MSR Wait state to cpu_idle loop
> 
> This patch sets the wait state MSR when in the cpu_idle loop. This is
> mainly to help out virtualization solutions such as KVM. This way the
> virtualization soultion is able to tell if the guest kernel is idle.
> 
> Signed-off-by: Jerone Young <jyoung5@us.ibm.com>
> 
> diff --git a/arch/powerpc/kernel/idle.c b/arch/powerpc/kernel/idle.c
> --- a/arch/powerpc/kernel/idle.c
> +++ b/arch/powerpc/kernel/idle.c
> @@ -32,6 +32,8 @@
>  #include <asm/time.h>
>  #include <asm/machdep.h>
>  #include <asm/smp.h>
> +
> +static unsigned long msr_save;

Why is this global?

>  #ifdef CONFIG_HOTPLUG_CPU
>  /* this is used for software suspend, and that shuts down
> @@ -88,6 +90,10 @@ void cpu_idle(void)
>  				HMT_low();
>  				HMT_very_low();
>  			}
> +
> +			/* set wait state MSR */
> +			msr_save = mfmsr();
> +			mtmsr(msr_save|MSR_WE);
>  		}
> 
>  		HMT_medium();

The code you are modifying is common to all PowerPC kernels. Why didn't
you use the power_save() hook provided to you?

-- 
Hollis Blanchard
IBM Linux Technology Center


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