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

[Zhoujian (jay)]

Hi Wanpeng,

> 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.

 In our tests, this branch is taken when living migration is successful.
 AFAIK, the kmod does not know whether living migration successful or not
 when dealing with KVM_SET_USER_MEMORY_REGION ioctl. Do I miss something?

Regards,
Jay Zhou