Re: [PATCH 4 of 5] kvm: ppc: Write only modified shadow entries into

[Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>]

Liu Yu wrote:
>
>   
>> -----Original Message-----
>> From: kvm-ppc-owner@vger.kernel.org 
>> [mailto:kvm-ppc-owner@vger.kernel.org] On Behalf Of Hollis Blanchard
>> Sent: Saturday, July 26, 2008 2:55 AM
>> To: avi@qumranet.com
>> Cc: kvm-ppc@vger.kernel.org; kvm@vger.kernel.org
>> Subject: [PATCH 4 of 5] kvm: ppc: Write only modified shadow 
>> entries into theTLB on exit
>>
>> @@ -229,6 +235,7 @@ void kvmppc_mmu_priv_switch(struct kvm_v
>>  
>>  		kvmppc_44x_shadow_release(vcpu, i);
>>  		stlbe->word0 = 0;
>> +		kvmppc_tlbe_set_modified(vcpu, i);
>>  		KVMTRACE_5D(STLB_INVAL, vcpu, i,
>>  				stlbe->tid, stlbe->word0, stlbe->word1,
>>  				stlbe->word2, handler);
>>     
>
> Can this place use "_tlbia()" instead?
>   
Hi Liu,
when we exit&reenter a guest on the lightweight path this patch saves us 
from rebuilding too much of the tlb.
It's just the point of the patch to not invalidate all tlb entries on 
every exit, but keeping as much as possible.
Additionally I'm not even sure if tlbia is available on all cores used.

Am I overlooking something ? - what do you think would be the benefit of 
using _tlbia() here?
Do you mean the loop to clear up to the hwater mark where this patch 
makes changes and not this patch itself?

-- 

Grüsse / regards, 
Christian Ehrhardt
IBM Linux Technology Center, Open Virtualization