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

[Wanpeng Li]

2017-05-17 15:43 GMT+08:00 Paolo Bonzini <address@hidden>:
>> Recently, I have tested the performance before migration and after migration 
>> failure
>> using spec cpu2006 https://www.spec.org/cpu2006/, which is a standard 
>> performance
>> evaluation tool.
>>
>> These are the steps:
>> ======
>>  (1) the version of kmod is 4.4.11(with slightly modified) and the version of
>>  qemu is 2.6.0
>>     (with slightly modified), the kmod is applied with the following patch
>>
>> diff --git a/source/x86/x86.c b/source/x86/x86.c
>> index 054a7d3..75a4bb3 100644
>> --- a/source/x86/x86.c
>> +++ b/source/x86/x86.c
>> @@ -8550,8 +8550,10 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
>>          */
>>         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);
>> +               !(new->flags & KVM_MEM_LOG_DIRTY_PAGES)) {
>> +               printk(KERN_ERR "zj make KVM_REQ_MMU_RELOAD request\n");
>> +               kvm_make_all_cpus_request(kvm, KVM_REQ_MMU_RELOAD);
>> +       }
>>
>>         /*
>>          * Set up write protection and/or dirty logging for the new slot.
>
> Try these modifications to the setup:
>
> 1) set up 1G hugetlbfs hugepages and use those for the guest's memory
>
> 2) test both without and with the above patch.
>

In addition, we can compare /sys/kernel/debug/kvm/largepages w/ and
w/o the patch. IIRC, /sys/kernel/debug/kvm/largepages will drop during
live migration, it will keep a small value if live migration fails and
w/o "lazy collapse small sptes into large sptes" codes, however, it
will increase gradually if w/ the "lazy collapse small sptes into
large sptes" codes.

Regards,
Wanpeng Li