linux-kernel - RE: about the time consuming kvm_vcpu

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Date:	Thu, 6 Aug 2015 05:58:36 +0000
From:	"Li, Liang Z" <liang.z.li@...el.com>
To:	Paolo Bonzini <pbonzini@...hat.com>,
	'Juan Quintela' <quintela@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:	"Zhang, Yang Z" <yang.z.zhang@...el.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: RE: about the time consuming kvm_vcpu_ioctl issue in rhel kernel

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'; linux-kernel@...r.kernel.org
> > Cc: Zhang, Yang Z; kvm@...r.kernel.org
> > 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
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