Re: [Xen-devel] [PATCH v2 COLOPre 03/13] libxc/restore: zero ioreq page only one time

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Wen Congyang [mailto:wency@xxxxxxxxxxxxxx]
> Sent: 12 June 2015 12:10
> To: Paul Durrant; Yang Hongyang; Andrew Cooper; xen-devel@xxxxxxxxxxxxx
> Cc: Wei Liu; Ian Campbell; guijianfeng@xxxxxxxxxxxxxx;
> yunhong.jiang@xxxxxxxxx; Eddie Dong; rshriram@xxxxxxxxx; Ian Jackson
> Subject: Re: [Xen-devel] [PATCH v2 COLOPre 03/13] libxc/restore: zero ioreq
> page only one time
> 
> On 06/12/2015 06:54 PM, Paul Durrant wrote:
> >> -----Original Message-----
> >> From: Wen Congyang [mailto:wency@xxxxxxxxxxxxxx]
> >> Sent: 12 June 2015 11:26
> >> To: Paul Durrant; Yang Hongyang; Andrew Cooper; xen-
> devel@xxxxxxxxxxxxx
> >> Cc: Wei Liu; Ian Campbell; guijianfeng@xxxxxxxxxxxxxx;
> >> yunhong.jiang@xxxxxxxxx; Eddie Dong; rshriram@xxxxxxxxx; Ian Jackson
> >> Subject: Re: [Xen-devel] [PATCH v2 COLOPre 03/13] libxc/restore: zero
> ioreq
> >> page only one time
> >>
> >> On 06/12/2015 03:41 PM, Paul Durrant wrote:
> >>>> -----Original Message-----
> >>>> From: Wen Congyang [mailto:wency@xxxxxxxxxxxxxx]
> >>>> Sent: 12 June 2015 04:22
> >>>> To: Paul Durrant; Yang Hongyang; Andrew Cooper; xen-
> >> devel@xxxxxxxxxxxxx
> >>>> Cc: Wei Liu; Ian Campbell; guijianfeng@xxxxxxxxxxxxxx;
> >>>> yunhong.jiang@xxxxxxxxx; Eddie Dong; rshriram@xxxxxxxxx; Ian Jackson
> >>>> Subject: Re: [Xen-devel] [PATCH v2 COLOPre 03/13] libxc/restore: zero
> >> ioreq
> >>>> page only one time
> >>>>
> >>>> On 06/11/2015 09:25 PM, Paul Durrant wrote:
> >>>>>> -----Original Message-----
> >>>>>> From: Yang Hongyang [mailto:yanghy@xxxxxxxxxxxxxx]
> >>>>>> Sent: 11 June 2015 13:59
> >>>>>> To: Paul Durrant; Wen Congyang; Andrew Cooper; xen-
> >>>> devel@xxxxxxxxxxxxx
> >>>>>> Cc: Wei Liu; Ian Campbell; guijianfeng@xxxxxxxxxxxxxx;
> >>>>>> yunhong.jiang@xxxxxxxxx; Eddie Dong; rshriram@xxxxxxxxx; Ian
> Jackson
> >>>>>> Subject: Re: [Xen-devel] [PATCH v2 COLOPre 03/13] libxc/restore:
> zero
> >>>> ioreq
> >>>>>> page only one time
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>>> On 06/11/2015 06:20 PM, Paul Durrant wrote:
> >>>>>>>> -----Original Message-----
> >>>>>>>> From: Wen Congyang [mailto:wency@xxxxxxxxxxxxxx]
> >>>>>>>> Sent: 11 June 2015 09:48
> >>>>>>>> To: Paul Durrant; Andrew Cooper; Yang Hongyang; xen-
> >>>>>> devel@xxxxxxxxxxxxx
> >>>>>>>> Cc: Wei Liu; Ian Campbell; guijianfeng@xxxxxxxxxxxxxx;
> >>>>>> [...]
> >>>>>>>
> >>>>>>>>
> >>>>>>>> In our implementation, we don't start a new emulator. The codes
> >> can
> >>>>>> work,
> >>>>>>>> but some bugs may be not triggered.
> >>>>>>>>
> >>>>>>>
> >>>>>>> How do you reconcile the incoming QEMU save record with the
> >> running
> >>>>>> emulator state?
> >>>>>>
> >>>>>> We introduce a qmp command "xen-load-devices-
> >>>>>> state"(libxl__qmp_restore) which
> >>>>>> can restore the emulator state. The step of resotre emulator state at
> a
> >>>>>> checkpoint is:
> >>>>>>
> >>>>>> 1. libxl__qmp_stop    -> vm_stop() in qemu
> >>>>>> 2. libxl__qmp_restore -> load_vmstate() in qemu
> >>>>>> 3. libxl__qmp_resume  -> vm_start() in qemu
> >>>>>>
> >>>>>
> >>>>> Ok, that sounds like the ideal time to hook back into Xen by creating a
> >> new
> >>>> ioreq server.
> >>>>
> >>>> I have some questions about ioreq server:
> >>>> 1. If we use old version xen and newest version qemu, is it OK? Is
> default
> >>>>    ioreq server created when the guest is created.
> >> xen_create_ioreq_server()
> >>>> does
> >>>>    nothing, and xen_get_ioreq_server_info() will get the default ioreq
> >> server
> >>>> information.
> >>>>    Is it right?
> >>>
> >>> No. It's not compatible in that direction. A new Xen will work with an old
> >> QEMU but not the other way round.
> 
> If the xen is newest, and qemu is old, how is the default ioreq server created
> for the emulator? Will the old qemu call xc_get_hvm_param(), and the
> hypervisor
> then creates a default ioreq server?
> get is a 'readonly' operation, and creating the default ioreq server in it is
> very strange.
> 

Might be strange, but that's the way it's done.

> >>>
> >>>> 2. Why we create a default ioreq server when getting the hvm param if
> >> there
> >>>> is already a
> >>>>    not default ioreq server?
> >>>
> >>> If something reads the 'legacy' HVM params then that is Xen's trigger to
> >> create the default server. Any 'new' emulator should be using the ioreq
> >> server hypercalls so the default server will not be needed.
> >>
> >> If there are two ioreq servers: default ioreq server, and a ioreq server
> >> created by emulator. The guest can work it correctly in
> >> this case?
> >
> > You mean a secondary emulator? Yes, that's why there is the notion of
> default ioreq server... to allow a secondary emulator to be used even when
> an old QEMU is in use.
> 
> No, only one emulator. Can we run more than one emulator for one hvm
> guest? How
> to do it?
> 

Yes, more than one emulator can run. There's nothing in libxl to do it, but we 
do it in XenServer using XAPI.

> >
> >> Is there any application(not emulator) that uses the libxenctrl
> >> directly?
> >>
> >
> > What do you mean by application? Toolstacks may use libxenctrl.
> 
> For example: libvirt. I know it uses libxl now. Is there any similar 
> application
> which uses libxenctrl.

Well, XAPI uses it for one.

  Paul

> 
> Thanks
> Wen Congyang
> 
> >
> >   Paul
> >
> >> Thanks
> >> Wen Congyang
> >>
> >>>
> >>>> 3. In the far end, we will clear the ioreq page, and this ioreq page is
> used
> >> for
> >>>> default
> >>>>    ioreq server, is it right?
> >>>
> >>> Yes, AFAIK it's only the 'magic' pages that get cleared at the far end - 
> >>> and
> >> that includes the default server pages. Other ioreq servers will have their
> >> pages cleared on re-insertion to the P2M at the source end when the
> server
> >> is disabled.
> >>>
> >>>   Paul
> >>>
> >>>>
> >>>> Thanks
> >>>> Wen Congyang
> >>>>
> >>>>>
> >>>>>   Paul
> >>>>>
> >>>>>>>
> >>>>>>>    Paul
> >>>>>>>
> >>>>>>>> Thanks
> >>>>>>>> Wen Congyang
> >>>>>>>>
> >>>>>>>>>
> >>>>>>>>>    Paul
> >>>>>>>>>
> >>>>>>>>>>
> >>>>>>>>>> Thanks
> >>>>>>>>>> Wen Congyang
> >>>>>>>>>>
> >>>>>>>>>>>
> >>>>>>>>>>>    Paul
> >>>>>>>>>>>
> >>>>>>>>>>>> We will set to the guest to a new state, the old state should
> be
> >>>>>>>> dropped.
> >>>>>>>>>>>>
> >>>>>>>>>>>> Thanks
> >>>>>>>>>>>> Wen Congyang
> >>>>>>>>>>>>
> >>>>>>>>>>>>>
> >>>>>>>>>>>>>    Paul
> >>>>>>>>>>>>>
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> Thanks
> >>>>>>>>>>>>>> Wen Congyang
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>    Paul
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>> Thanks
> >>>>>>>>>>>>>>>> Wen Congyang
> >>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>> ~Andrew
> >>>>>>>>>>>>>>>>> .
> >>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>> .
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> .
> >>>>>>>>>>>>>
> >>>>>>>>>>>>
> >>>>>>>>>>>>
> >>>>>>>>>>>>
> _______________________________________________
> >>>>>>>>>>>> Xen-devel mailing list
> >>>>>>>>>>>> Xen-devel@xxxxxxxxxxxxx
> >>>>>>>>>>>> http://lists.xen.org/xen-devel
> >>>>>>>>>>>
> >>>>>>>>>>> _______________________________________________
> >>>>>>>>>>> Xen-devel mailing list
> >>>>>>>>>>> Xen-devel@xxxxxxxxxxxxx
> >>>>>>>>>>> http://lists.xen.org/xen-devel
> >>>>>>>>>>> .
> >>>>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> .
> >>>>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>> _______________________________________________
> >>>>>>> Xen-devel mailing list
> >>>>>>> Xen-devel@xxxxxxxxxxxxx
> >>>>>>> http://lists.xen.org/xen-devel
> >>>>>>> .
> >>>>>>>
> >>>>>>
> >>>>>> --
> >>>>>> Thanks,
> >>>>>> Yang.
> >>>>> .
> >>>>>
> >>>
> >>> .
> >>>
> >
> > .
> >


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