Re: [kvm-devel] [PATCH 0/5] KVM paravirt_ops backend (v3)

[Anthony L. <an...@co...>]

Avi Kivity wrote:
> Anthony Liguori wrote:
>> Hi,
>>
>> This is an update to the paravirt_ops KVM backend series.  I've made 
>> a number of changes and attempted to incorporate all the feedback 
>> from the last review.  Some highlights:
>>
>> 1) Clean up the paravirt time source patch to use a more Xen-like model
>> 2) Change the hypercall queueing to pass a PA on the flush hypercall
>> 3) Add MMU support for release_{pt,pd} and TLB flush
>> 4) Use KVM specific errno values
>> 5) Switch from per_cpu to more appropriate functions
>>
>> As for performance, I've got a few interesting results.  kbuild with 
>> a guest using 2G of memory goes from 19 minutes to 12 minutes with 
>> the full series applied.  Using 512mb, the build time goes from 10.75 
>> minutes to 9 minutes.  For 512mb, native is around 7 minutes so 
>> that's pretty close to what Avi had seen.  The more dramatic 
>> improvement with large memory guests is probably because of the 
>> increased shadow page table activity due to high mem.
>
> Ah, that explains why we were getting such different results.  My 
> tests were on x86-64.
>
>>
>> virtbench shows major improvements but I'm not 100% confident yet in 
>> the results as they are not very stable.  I don't yet have a 
>> benchmark that shows the benefit of the CR caching so if I don't find 
>> one, I'll drop that from the queue.
>>
>
> The only barrier to merging is that we're introducing yet another 
> stable ABI.  Since we can turn off things that turn out not so good 
> later, and expect the guest to survive, I'm not to worried, so I'm 
> inclined to merge this.

Some unsigned longs are in kvm_para.h so x86_64 won't work ATM as a 
host.  I'll fix that and do proper testing on a 64 bit host for the next 
posting (along with save/restore support).

Regards,

Anthony Liguori