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Wed, 27 May 2020 08:48:24 +0000 (UTC) Date: Wed, 27 May 2020 09:48:22 +0100 From: "Dr. David Alan Gilbert" To: Yan Zhao Subject: Re: [PATCH Kernel v22 0/8] Add UAPIs to support migration for VFIO devices Message-ID: <20200527084822.GC3001@work-vm> References: <1589781397-28368-1-git-send-email-kwankhede@nvidia.com> <20200519105804.02f3cae8@x1.home> <20200525065925.GA698@joy-OptiPlex-7040> <426a5314-6d67-7cbe-bad0-e32f11d304ea@nvidia.com> <20200526141939.2632f100@x1.home> <20200527062358.GD19560@joy-OptiPlex-7040> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200527062358.GD19560@joy-OptiPlex-7040> User-Agent: Mutt/1.13.4 (2020-02-15) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Received-SPF: pass client-ip=205.139.110.120; envelope-from=dgilbert@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/27 00:49:35 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_PASS=-0.001, T_HK_NAME_DR=0.01, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN X-Spam_action: no action 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, kevin.tian@intel.com, yi.l.liu@intel.com, cjia@nvidia.com, kvm@vger.kernel.org, eskultet@redhat.com, ziye.yang@intel.com, qemu-devel@nongnu.org, cohuck@redhat.com, shuangtai.tst@alibaba-inc.com, Kirti Wankhede , zhi.a.wang@intel.com, mlevitsk@redhat.com, pasic@linux.ibm.com, aik@ozlabs.ru, Alex Williamson , eauger@redhat.com, felipe@nutanix.com, jonathan.davies@nutanix.com, changpeng.liu@intel.com, 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, May 26, 2020 at 02:19:39PM -0600, Alex Williamson wrote: > > On Mon, 25 May 2020 18:50:54 +0530 > > Kirti Wankhede wrote: > > > > > On 5/25/2020 12:29 PM, Yan Zhao wrote: > > > > On Tue, May 19, 2020 at 10:58:04AM -0600, Alex Williamson wrote: > > > >> Hi folks, > > > >> > > > >> My impression is that we're getting pretty close to a workable > > > >> implementation here with v22 plus respins of patches 5, 6, and 8. We > > > >> also have a matching QEMU series and a proposal for a new i40e > > > >> consumer, as well as I assume GVT-g updates happening internally at > > > >> Intel. I expect all of the latter needs further review and discussion, > > > >> but we should be at the point where we can validate these proposed > > > >> kernel interfaces. Therefore I'd like to make a call for reviews so > > > >> that we can get this wrapped up for the v5.8 merge window. I know > > > >> Connie has some outstanding documentation comments and I'd like to make > > > >> sure everyone has an opportunity to check that their comments have been > > > >> addressed and we don't discover any new blocking issues. Please send > > > >> your Acked-by/Reviewed-by/Tested-by tags if you're satisfied with this > > > >> interface and implementation. Thanks! > > > >> > > > > hi Alex > > > > after porting gvt/i40e vf migration code to kernel/qemu v23, we spoted > > > > two bugs. > > > > 1. "Failed to get dirty bitmap for iova: 0xfe011000 size: 0x3fb0 err: 22" > > > > This is a qemu bug that the dirty bitmap query range is not the same > > > > as the dma map range. It can be fixed in qemu. and I just have a little > > > > concern for kernel to have this restriction. > > > > > > > > > > I never saw this unaligned size in my testing. In this case if you can > > > provide vfio_* event traces, that will helpful. > > > > Yeah, I'm curious why we're hitting such a call path, I think we were > > designing this under the assumption we wouldn't see these. I also > that's because the algorithm for getting dirty bitmap query range is still not exactly > matching to that for dma map range in vfio_dma_map(). > > > > wonder if we really need to enforce the dma mapping range for getting > > the dirty bitmap with the current implementation (unmap+dirty obviously > > still has the restriction). We do shift the bitmap in place for > > alignment, but I'm not sure why we couldn't shift it back and only > > clear the range that was reported. Kirti, do you see other issues? I > > think a patch to lift that restriction is something we could plan to > > include after the initial series is included and before we've committed > > to the uapi at the v5.8 release. > > > > > > 2. migration abortion, reporting > > > > "qemu-system-x86_64-lm: vfio_load_state: Error allocating buffer > > > > qemu-system-x86_64-lm: error while loading state section id 49(vfio) > > > > qemu-system-x86_64-lm: load of migration failed: Cannot allocate memory" > > > > > > > > It's still a qemu bug and we can fixed it by > > > > " > > > > if (migration->pending_bytes == 0) { > > > > + qemu_put_be64(f, 0); > > > > + qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE); > > > > " > > > > > > In which function in QEMU do you have to add this? > > > > I think this is relative to QEMU path 09/ where Yan had the questions > > below on v16 and again tried to get answers to them on v22: > > > > https://lore.kernel.org/qemu-devel/20200520031323.GB10369@joy-OptiPlex-7040/ > > > > Kirti, please address these questions. > > > > > > and actually there are some extra concerns about this part, as reported in > > > > [1][2]. > > > > > > > > [1] data_size should be read ahead of data_offset > > > > https://lists.gnu.org/archive/html/qemu-devel/2020-05/msg02795.html. > > > > [2] should not repeatedly update pending_bytes in vfio_save_iterate() > > > > https://lists.gnu.org/archive/html/qemu-devel/2020-05/msg02796.html. > > > > > > > > but as those errors are all in qemu, and we have finished basic tests in > > > > both gvt & i40e, we're fine with the kernel part interface in general now. > > > > (except for my concern [1], which needs to update kernel patch 1) > > > > > > > > > > >> what if pending_bytes is not 0, but vendor driver just does not want to > > > >> send data in this iteration? isn't it right to get data_size first > > > before > > > >> getting data_offset? > > > > > > If vendor driver doesn't want to send data but still has data in staging > > > buffer, vendor driver still can control to send pending_bytes for this > > > iteration as 0 as this is a trap field. > > > > > > I would defer this to Alex. > > > > This is my understanding of the protocol as well, when the device is > > running, pending_bytes might drop to zero if no internal state has > > changed and may be non-zero on the next iteration due to device > > activity. When the device is not running, pending_bytes reporting zero > > indicates the device is done, there is no further state to transmit. > > Does that meet your need/expectation? > > > (1) on one side, as in vfio_save_pending(), > vfio_save_pending() > { > ... > ret = vfio_update_pending(vbasedev); > ... > *res_precopy_only += migration->pending_bytes; > ... > } > the pending_bytes tells migration thread how much data is still hold in > device side. > the device data includes > device internal data + running device dirty data + device state. > > so the pending_bytes should include device state as well, right? > if so, the pending_bytes should never reach 0 if there's any device > state to be sent after device is stopped. I hadn't expected the pending-bytes to include a fixed offset for device state (If you mean a few registers etc) - I'd expect pending to drop possibly to zero; the heuristic as to when to switch from iteration to stop, is based on the total pending across all iterated devices; so it's got to be allowed to drop otherwise you'll never transition to stop. > (2) on the other side, > along side we updated the pending_bytes in vfio_save_pending() and > enter into the vfio_save_iterate(), if we repeatedly update > pending_bytes in vfio_save_iterate(), it would enter into a scenario > like > > initially pending_bytes=500M. > vfio_save_iterate() --> > round 1: transmitted 500M. > round 2: update pending bytes, pending_bytes=50M (50M dirty data). > round 3: update pending bytes, pending_bytes=50M. > ... > round N: update pending bytes, pending_bytes=50M. > > If there're two vfio devices, the vfio_save_iterate() for the second device > may never get chance to be called because there's always pending_bytes > produced by the first device, even the size if small. And between RAM and the vfio devices? > > > > so I wonder which way in your mind is better, to give our reviewed-by to > > > > the kernel part now, or hold until next qemu fixes? > > > > and as performance data from gvt is requested from your previous mail, is > > > > that still required before the code is accepted? > > > > The QEMU series does not need to be perfect, I kind of expect we might > > see a few iterations of that beyond the kernel portion being accepted. > > We should have the QEMU series to the point that we've resolved any > > uapi issues though, which it seems like we're pretty close to having. > > Ideally I'd like to get the kernel series into my next branch before > > the merge window opens, where it seems like upstream is on schedule to > > have that happen this Sunday. If you feel we're to the point were we > > can iron a couple details out during the v5.8 development cycle, then > > please provide your reviewed-by. We haven't fully committed to a uapi > > until we've committed to it for a non-rc release. > > > got it. > > > I think the performance request was largely due to some conversations > > with Dave Gilbert wondering if all this actually works AND is practical > > for a LIVE migration. I think we're all curious about things like how > > much data does a GPU have to transfer in each phase of migration, and > > particularly if the final phase is going to be a barrier to claiming > > the VM is actually sufficiently live. I'm not sure we have many > > options if a device simply has a very large working set, but even > > anecdotal evidence that the stop-and-copy phase transfers abMB from the > > device while idle or xyzMB while active would give us some idea what to > for intel vGPU, the data is > single-round dirty query: > data to be transferred at stop-and-copy phase: 90MB+ ~ 900MB+, including > - device state: 9MB > - system dirty memory: 80MB+ ~ 900MB+ (depending on workload type) > > multi-round dirty query : > -each iteration data: 60MB ~ 400MB > -data to be transferred at stop-and-copy phase: 70MB ~ 400MB > > > > BTW, for viommu, the downtime data is as below. under the same network > condition and guest memory size, and no running dirty data/memory produced > by device. > (1) viommu off > single-round dirty query: downtime ~100ms Fine. > (2) viommu on > single-round dirty query: downtime 58s Youch. Dave > > Thanks > Yan > > expect. Kirti, have you done any of those sorts of tests for NVIDIA's > > driver? > > > > > > BTW, we have also conducted some basic tests when viommu is on, and found out > > > > errors like > > > > "qemu-system-x86_64-dt: vtd_iova_to_slpte: detected slpte permission error (iova=0x0, level=0x3, slpte=0x0, write=1) > > > > qemu-system-x86_64-dt: vtd_iommu_translate: detected translation failure (dev=00:03:00, iova=0x0) > > > > qemu-system-x86_64-dt: New fault is not recorded due to compression of faults". > > > > > > > > > > I saw these errors, I'm looking into it. > > > > Let's try to at least determine if this is a uapi issue or just a QEMU > > implementation bug for progressing the kernel series. Thanks, > > > > Alex > > > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK