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

[Wen Congyang <ghostwcy@xxxxxxxxx>]

At 2015/6/12 19:48, Paul Durrant Wrote:
> > -----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.
If I only want to get the default ioreq server pfn, and don't want to 
create the default
ioreq server, how can I do it?

Thanks
Wen Congyang

> > > > > > 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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