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Fri, 28 Jun 2019 09:44:56 +0000 (UTC) Received: from work-vm (ovpn-116-169.ams2.redhat.com [10.36.116.169]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C067860922; Fri, 28 Jun 2019 09:44:49 +0000 (UTC) Date: Fri, 28 Jun 2019 10:44:47 +0100 From: "Dr. David Alan Gilbert" To: Yan Zhao Message-ID: <20190628094447.GD2922@work-vm> References: <1561041461-22326-1-git-send-email-kwankhede@nvidia.com> <20190621002518.GF9303@joy-OptiPlex-7040> <20190621012404.GA4173@joy-OptiPlex-7040> <67726e08-f159-7054-57a7-36b08f691756@nvidia.com> <20190621084627.GC4304@joy-OptiPlex-7040> <583faf0d-55e7-0611-3e1c-b4925ca7e533@nvidia.com> <20190624190024.GX2726@work-vm> <20190626004303.GF6971@joy-OptiPlex-7040> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190626004303.GF6971@joy-OptiPlex-7040> User-Agent: Mutt/1.12.0 (2019-05-25) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Fri, 28 Jun 2019 09:44:56 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH v4 00/13] Add migration support for VFIO device X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Zhengxiao.zx@Alibaba-inc.com" , "Tian, Kevin" , "Liu, Yi L" , "cjia@nvidia.com" , "eskultet@redhat.com" , "Yang, Ziye" , "qemu-devel@nongnu.org" , "cohuck@redhat.com" , "shuangtai.tst@alibaba-inc.com" , "alex.williamson@redhat.com" , "Wang, Zhi A" , "mlevitsk@redhat.com" , "pasic@linux.ibm.com" , "aik@ozlabs.ru" , Kirti Wankhede , "eauger@redhat.com" , "felipe@nutanix.com" , "jonathan.davies@nutanix.com" , "Liu, Changpeng" , "Ken.Xue@amd.com" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Yan Zhao (yan.y.zhao@intel.com) wrote: > On Tue, Jun 25, 2019 at 03:00:24AM +0800, Dr. David Alan Gilbert wrote: > > * Kirti Wankhede (kwankhede@nvidia.com) 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. 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. 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 / dgilbert@redhat.com / Manchester, UK -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK