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

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On 15.09.2011, at 23:36, Scott Wood wrote:

> 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).

Since we're PV'ing here either way, can't we simply define a generic power_save implementation that works across different CPU types? We could for example always use EV_IDLE.


Alex

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