Re: [PATCH 4/5] KVM: PPC: e500: eliminate a trap when entering idle

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On 09/05/2011 05:30 PM, Alexander Graf wrote:
> 
> On 27.08.2011, at 01:31, Scott Wood wrote:
> 
>> +#ifdef CONFIG_E500
>> +	/*
>> +	 * Skip the overhead of HID0 accesses that KVM ignores --
>> +	 * just write MSR[WE].
>> +	 *
>> +	 * We don't need _TLF_NAPPING, because under KVM we know
>> +	 * it will take effect right away.
>> +	 */
>> +	if (ppc_md.power_save == e500_idle)
>> +		ppc_md.power_save = kvm_msrwe_idle;
> 
> Why the if() here?

To avoid replacing some other power_save() implementation.
kvm_msrwe_idle() is a paravirt-optimized version of e500_idle().

However, now that e500_idle has an ifdef for e500mc, we'll need that
ifdef here as well.  e500mc doesn't use MSR[WE] (and if it did, we
couldn't trap on it).  For e500mc we'll want to make an hcall for idle
(ePAPR EV_IDLE).

-Scott

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