Hi Paolo & Juan,
I found some of the kvm_vcpu_ioctl operation takes about more than 10ms with the 3.10.0-229.el7.x86_64 kernel, which prolong the VM service downtime when doing live migration about 20~30ms.
This happened when doing the KVM_KVMCLOCK_CTRL ioctl. It's worse if more VCPUs used by guest(4VPUs in my test). The upstream kernel does not have this issue because of the patch 7a72f7a140bfd3,
maybe this patch should be backported to the el7 kernel.
Liang
The synchronize_rcu() is a time consuming operation, the unpstream kernel still have some issue, the KVM_RUN ioctl will take more then 10ms when resume the VM after migration.
Liang
> -----Original Message-----
> From: Li, Liang Z
> Sent: Thursday, August 06, 2015 11:47 AM
> To: 'Paolo Bonzini'; 'Juan Quintela'; [email protected]
> Cc: Zhang, Yang Z; [email protected]
> Subject: about the time consuming kvm_vcpu_ioctl issue in rhel kernel
>
> Hi Paolo & Juan,
>
> I found some of the kvm_vcpu_ioctl operation takes about more than 10ms
> with the 3.10.0-229.el7.x86_64 kernel, which prolong the VM service
> downtime when doing live migration about 20~30ms.
> This happened when doing the KVM_KVMCLOCK_CTRL ioctl. It's worse if
> more VCPUs used by guest(4VPUs in my test). The upstream kernel does not
> have this issue because of the patch 7a72f7a140bfd3, maybe this patch
> should be backported to the el7 kernel.
>
> Liang
Please Ignore the following message in the brace
{ The synchronize_rcu() is a time consuming operation, the unpstream kernel
still have some issue, the KVM_RUN ioctl will take more then 10ms when
resume the VM after migration. }
The upstream kernel does not have such issue, only the rhel kernel has. Forgive my neglect.
Liang
>
>
> > -----Original Message-----
> > From: Li, Liang Z
> > Sent: Thursday, August 06, 2015 11:47 AM
> > To: 'Paolo Bonzini'; 'Juan Quintela'; [email protected]
> > Cc: Zhang, Yang Z; [email protected]
> > Subject: about the time consuming kvm_vcpu_ioctl issue in rhel kernel
> >
> > Hi Paolo & Juan,
> >
> > I found some of the kvm_vcpu_ioctl operation takes about more than
> > 10ms with the 3.10.0-229.el7.x86_64 kernel, which prolong the VM
> > service downtime when doing live migration about 20~30ms.
> > This happened when doing the KVM_KVMCLOCK_CTRL ioctl. It's worse if
> > more VCPUs used by guest(4VPUs in my test). The upstream kernel does
> > not have this issue because of the patch 7a72f7a140bfd3, maybe this
> > patch should be backported to the el7 kernel.
> >
> > Liang