Re: [Qemu-devel] About QEMU BQL and dirty log switch in Migration

[Wanpeng Li]

2017-05-11 21:43 GMT+08:00 Wanpeng Li <address@hidden>:
> 2017-05-11 20:24 GMT+08:00 Paolo Bonzini <address@hidden>:
>>
>>
>> On 11/05/2017 14:07, Zhoujian (jay) wrote:
>>> -        * Scan sptes if dirty logging has been stopped, dropping those
>>> -        * which can be collapsed into a single large-page spte.  Later
>>> -        * page faults will create the large-page sptes.
>>> +        * Reset each vcpu's mmu, then page faults will create the 
>>> large-page
>>> +        * sptes later.
>>>          */
>>>         if ((change != KVM_MR_DELETE) &&
>>>                 (old->flags & KVM_MEM_LOG_DIRTY_PAGES) &&
>>> -               !(new->flags & KVM_MEM_LOG_DIRTY_PAGES))
>>> -               kvm_mmu_zap_collapsible_sptes(kvm, new);
>
> This is an unlikely branch(unless guest live migration fails and
> continue to run on the source machine) instead of hot path, do you
> have any performance number for your real workloads?

I find the original discussion by google.
https://lists.nongnu.org/archive/html/qemu-devel/2017-04/msg04143.html
You will not go to this branch if the guest live migration
successfully.

Regards,
Wanpeng Li