[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH v4 00/13] Add migration support for VFIO device
From: |
Yan Zhao |
Subject: |
Re: [Qemu-devel] [PATCH v4 00/13] Add migration support for VFIO device |
Date: |
Fri, 28 Jun 2019 17:28:53 -0400 |
User-agent: |
Mutt/1.9.4 (2018-02-28) |
On Fri, Jun 28, 2019 at 05:44:47PM +0800, Dr. David Alan Gilbert wrote:
> * Yan Zhao (address@hidden) wrote:
> > On Tue, Jun 25, 2019 at 03:00:24AM +0800, Dr. David Alan Gilbert wrote:
> > > * Kirti Wankhede (address@hidden) wrote:
> > > >
> > > >
> > > > On 6/21/2019 2:16 PM, Yan Zhao wrote:
> > > > > On Fri, Jun 21, 2019 at 04:02:50PM +0800, Kirti Wankhede wrote:
> > > > >>
> > > > >>
> > > > >> On 6/21/2019 6:54 AM, Yan Zhao wrote:
> > > > >>> On Fri, Jun 21, 2019 at 08:25:18AM +0800, Yan Zhao wrote:
> > > > >>>> On Thu, Jun 20, 2019 at 10:37:28PM +0800, Kirti Wankhede wrote:
> > > > >>>>> Add migration support for VFIO device
> > > > >>>>>
> > > > >>>>> This Patch set include patches as below:
> > > > >>>>> - Define KABI for VFIO device for migration support.
> > > > >>>>> - Added save and restore functions for PCI configuration space
> > > > >>>>> - Generic migration functionality for VFIO device.
> > > > >>>>> * This patch set adds functionality only for PCI devices, but
> > > > >>>>> can be
> > > > >>>>> extended to other VFIO devices.
> > > > >>>>> * Added all the basic functions required for pre-copy,
> > > > >>>>> stop-and-copy and
> > > > >>>>> resume phases of migration.
> > > > >>>>> * Added state change notifier and from that notifier function,
> > > > >>>>> VFIO
> > > > >>>>> device's state changed is conveyed to VFIO device driver.
> > > > >>>>> * During save setup phase and resume/load setup phase,
> > > > >>>>> migration region
> > > > >>>>> is queried and is used to read/write VFIO device data.
> > > > >>>>> * .save_live_pending and .save_live_iterate are implemented to
> > > > >>>>> use QEMU's
> > > > >>>>> functionality of iteration during pre-copy phase.
> > > > >>>>> * In .save_live_complete_precopy, that is in stop-and-copy
> > > > >>>>> phase,
> > > > >>>>> iteration to read data from VFIO device driver is implemented
> > > > >>>>> till pending
> > > > >>>>> bytes returned by driver are not zero.
> > > > >>>>> * Added function to get dirty pages bitmap for the pages which
> > > > >>>>> are used by
> > > > >>>>> driver.
> > > > >>>>> - Add vfio_listerner_log_sync to mark dirty pages.
> > > > >>>>> - Make VFIO PCI device migration capable. If migration region is
> > > > >>>>> not provided by
> > > > >>>>> driver, migration is blocked.
> > > > >>>>>
> > > > >>>>> Below is the flow of state change for live migration where states
> > > > >>>>> in brackets
> > > > >>>>> represent VM state, migration state and VFIO device state as:
> > > > >>>>> (VM state, MIGRATION_STATUS, VFIO_DEVICE_STATE)
> > > > >>>>>
> > > > >>>>> Live migration save path:
> > > > >>>>> QEMU normal running state
> > > > >>>>> (RUNNING, _NONE, _RUNNING)
> > > > >>>>> |
> > > > >>>>> migrate_init spawns migration_thread.
> > > > >>>>> (RUNNING, _SETUP, _RUNNING|_SAVING)
> > > > >>>>> Migration thread then calls each device's .save_setup()
> > > > >>>>> |
> > > > >>>>> (RUNNING, _ACTIVE, _RUNNING|_SAVING)
> > > > >>>>> If device is active, get pending bytes by .save_live_pending()
> > > > >>>>> if pending bytes >= threshold_size, call save_live_iterate()
> > > > >>>>> Data of VFIO device for pre-copy phase is copied.
> > > > >>>>> Iterate till pending bytes converge and are less than
> > > > >>>>> threshold
> > > > >>>>> |
> > > > >>>>> On migration completion, vCPUs stops and calls
> > > > >>>>> .save_live_complete_precopy
> > > > >>>>> for each active device. VFIO device is then transitioned in
> > > > >>>>> _SAVING state.
> > > > >>>>> (FINISH_MIGRATE, _DEVICE, _SAVING)
> > > > >>>>> For VFIO device, iterate in .save_live_complete_precopy
> > > > >>>>> until
> > > > >>>>> pending data is 0.
> > > > >>>>> (FINISH_MIGRATE, _DEVICE, _STOPPED)
> > > > >>>>
> > > > >>>> I suggest we also register to VMStateDescription, whose .pre_save
> > > > >>>> handler would get called after .save_live_complete_precopy in
> > > > >>>> pre-copy
> > > > >>>> only case, and will called before .save_live_iterate in post-copy
> > > > >>>> enabled case.
> > > > >>>> In the .pre_save handler, we can save all device state which must
> > > > >>>> be
> > > > >>>> copied after device stop in source vm and before device start in
> > > > >>>> target vm.
> > > > >>>>
> > > > >>> hi
> > > > >>> to better describe this idea:
> > > > >>>
> > > > >>> in pre-copy only case, the flow is
> > > > >>>
> > > > >>> start migration --> .save_live_iterate (several round) -> stop
> > > > >>> source vm
> > > > >>> --> .save_live_complete_precopy --> .pre_save -->start target vm
> > > > >>> -->migration complete
> > > > >>>
> > > > >>>
> > > > >>> in post-copy enabled case, the flow is
> > > > >>>
> > > > >>> start migration --> .save_live_iterate (several round) --> start
> > > > >>> post copy -->
> > > > >>> stop source vm --> .pre_save --> start target vm -->
> > > > >>> .save_live_iterate (several round)
> > > > >>> -->migration complete
> > > > >>>
> > > > >>> Therefore, we should put saving of device state in .pre_save
> > > > >>> interface
> > > > >>> rather than in .save_live_complete_precopy.
> > > > >>> The device state includes pci config data, page tables, register
> > > > >>> state, etc.
> > > > >>>
> > > > >>> The .save_live_iterate and .save_live_complete_precopy should only
> > > > >>> deal
> > > > >>> with saving dirty memory.
> > > > >>>
> > > > >>
> > > > >> Vendor driver can decide when to save device state depending on the
> > > > >> VFIO
> > > > >> device state set by user. Vendor driver doesn't have to depend on
> > > > >> which
> > > > >> callback function QEMU or user application calls. In pre-copy case,
> > > > >> save_live_complete_precopy sets VFIO device state to
> > > > >> VFIO_DEVICE_STATE_SAVING which means vCPUs are stopped and vendor
> > > > >> driver
> > > > >> should save all device state.
> > > > >>
> > > > > when post copy stops vCPUs and vfio device, vendor driver only needs
> > > > > to
> > > > > provide device state. but how vendor driver knows that, if no extra
> > > > > interface or no extra device state is provides?
> > > > >
> > > >
> > > > .save_live_complete_postcopy interface for post-copy will get called,
> > > > right?
> > >
> > > That happens at the very end; I think the question here is for something
> > > that gets called at the point we stop iteratively sending RAM, send the
> > > device states and then start sending RAM on demand to the destination
> > > as it's running. Typically we send a small set of device state
> > > (registers etc) at this point.
> > >
> > > I guess there's two different postcopy cases that we need to think
> > > about:
> > > a) Where the VFIO device doesn't support postcopy - it just gets
> > > migrated like any other device, so all it's RAM must get sent
> > > before we flip into postcopy mode.
> > >
> > > b) Where the VFIO device does support postcopy - where the pages
> > > get sent on demand.
> > >
> > > (b) maybe tricky depending on whether your hardware can fault
> > > on pages of your RAM that are needed but not yet transferred; but
> > > if you can that would make life a lot more practical on really
> > > big VFO devices.
> > >
> > > Dave
> > >
> > hi Dave,
> > so do you think it is good to abstract device state data and save it in
> > .pre_save callback?
>
> I'm not sure we have a vmsd/pre_save in this setup? If we did then it's
> a bit confusing because I don't think we have any other iterative device
> that also has a vmsd.
Yes, I tried it. it's ok to register SaveVMHandlers and VMStateDescription at
the
same time.
>
> I'd have to test it, but I think you might get the devices
> ->save_live_complete_precopy called at the right point just before
> postcopy switchover. It's worth looking.
>
if a iterative device supports postcopy, then its save_live_complete_precopy
would not get called before postcopy switchover.
However, postcopy may need to save pure device state only data (not memory) at
that
time. That's the reason I think we should also register to
VMStateDescription also, as its .pre_save handler would get called at
at that time.
Thanks
Yan
> Dave
>
> > Thanks
> > Yan
> >
> > > > Thanks,
> > > > Kirti
> > > >
> > > > >>>
> > > > >>> I know current implementation does not support post-copy. but at
> > > > >>> least
> > > > >>> it should not require huge change when we decide to enable it in
> > > > >>> future.
> > > > >>>
> > > > >>
> > > > >> .has_postcopy and .save_live_complete_postcopy need to be
> > > > >> implemented to
> > > > >> support post-copy. I think .save_live_complete_postcopy should be
> > > > >> similar to vfio_save_complete_precopy.
> > > > >>
> > > > >> Thanks,
> > > > >> Kirti
> > > > >>
> > > > >>> Thanks
> > > > >>> Yan
> > > > >>>
> > > --
> > > Dr. David Alan Gilbert / address@hidden / Manchester, UK
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK
- Re: [Qemu-devel] [PATCH v4 13/13] vfio: Add trace events in migration code path, (continued)
- Re: [Qemu-devel] [PATCH v4 00/13] Add migration support for VFIO device, Yan Zhao, 2019/06/20
- Re: [Qemu-devel] [PATCH v4 00/13] Add migration support for VFIO device, Yan Zhao, 2019/06/20
- Re: [Qemu-devel] [PATCH v4 00/13] Add migration support for VFIO device, Kirti Wankhede, 2019/06/21
- Re: [Qemu-devel] [PATCH v4 00/13] Add migration support for VFIO device, Yan Zhao, 2019/06/21
- Re: [Qemu-devel] [PATCH v4 00/13] Add migration support for VFIO device, Kirti Wankhede, 2019/06/21
- Re: [Qemu-devel] [PATCH v4 00/13] Add migration support for VFIO device, Yan Zhao, 2019/06/21
- Re: [Qemu-devel] [PATCH v4 00/13] Add migration support for VFIO device, Dr. David Alan Gilbert, 2019/06/24
- Re: [Qemu-devel] [PATCH v4 00/13] Add migration support for VFIO device, Yan Zhao, 2019/06/25
- Re: [Qemu-devel] [PATCH v4 00/13] Add migration support for VFIO device, Dr. David Alan Gilbert, 2019/06/28
- Re: [Qemu-devel] [PATCH v4 00/13] Add migration support for VFIO device,
Yan Zhao <=