linux-kernel - RE: about the time consuming kvm_vcpu

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Date:	Thu, 6 Aug 2015 05:38:23 +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

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'; 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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