Re: [Qemu-devel] [PATCH 0/5] QEMU VFIO live migration

[Zhao Yan <yan.y.zhao@intel.com>]

On Thu, Feb 21, 2019 at 03:16:45AM +0000, Gonglei (Arei) wrote:
> 
> 
> 
> > -----Original Message-----
> > From: Zhao Yan [mailto:yan.y.zhao@intel.com]
> > Sent: Thursday, February 21, 2019 10:05 AM
> > To: Gonglei (Arei) <arei.gonglei@huawei.com>
> > Cc: alex.williamson@redhat.com; qemu-devel@nongnu.org;
> > intel-gvt-dev@lists.freedesktop.org; Zhengxiao.zx@Alibaba-inc.com;
> > yi.l.liu@intel.com; eskultet@redhat.com; ziye.yang@intel.com;
> > cohuck@redhat.com; shuangtai.tst@alibaba-inc.com; dgilbert@redhat.com;
> > zhi.a.wang@intel.com; mlevitsk@redhat.com; pasic@linux.ibm.com;
> > aik@ozlabs.ru; eauger@redhat.com; felipe@nutanix.com;
> > jonathan.davies@nutanix.com; changpeng.liu@intel.com; Ken.Xue@amd.com;
> > kwankhede@nvidia.com; kevin.tian@intel.com; cjia@nvidia.com;
> > kvm@vger.kernel.org
> > Subject: Re: [PATCH 0/5] QEMU VFIO live migration
> > 
> > > >
> > > > > 5) About log sync, why not register log_global_start/stop in
> > > > vfio_memory_listener?
> > > > >
> > > > >
> > > > seems log_global_start/stop cannot be iterately called in pre-copy phase?
> > > > for dirty pages in system memory, it's better to transfer dirty data
> > > > iteratively to reduce down time, right?
> > > >
> > >
> > > We just need invoking only once for start and stop logging. Why we need to
> > call
> > > them literately? See memory_listener of vhost.
> > >
> > the dirty pages in system memory produces by device is incremental.
> > if it can be got iteratively, the dirty pages in stop-and-copy phase can be
> > minimal.
> > :)
> > 
> I mean starting or stopping the capability of logging, not log sync. 
> 
> We register the below callbacks:
> 
> .log_sync = vfio_log_sync,
> .log_global_start = vfio_log_global_start,
> .log_global_stop = vfio_log_global_stop,
>
.log_global_start is also a good point to notify logging state.
But if notifying in .save_setup handler, we can do fine-grained
control of when to notify of logging starting together with get_buffer
operation.
Is there any special benifit by registering to .log_global_start/stop?


> Regards,
> -Gonglei