Re: [Qemu-devel] [GSoC] Help needed in implementing live migration
* Stefan Hajnoczi (stefa...@gmail.com) wrote: > On Thu, Jun 27, 2019 at 05:02:33AM +0530, Sukrit Bhatnagar wrote: > > On Tue, 25 Jun 2019 at 00:11, Dr. David Alan Gilbert > > wrote: > > > > > > * Sukrit Bhatnagar (skrtbht...@gmail.com) wrote: > > > > Hi David, > > > > > > > > I am Sukrit, GSoC participant working on PVRDMA live migration. > > > > We had a short chat about vmxnet3 migration about a week ago > > > > on the IRC channel. > > > > > > > > I am facing an issue while doing migration of the pvrdma device. > > > > While loading the device state, we need to perform a few dma > > > > mappings on the destination. But on the destination, the migration > > > > fails due a BounceBuffer being locked (in_use). This global > > > > BounceBuffer is used in address_space_map/unmap functions > > > > which the rdma_pci_dma_map/unmap calls. > > > > Essentially, we need a way to remap guest physical address on > > > > the destination after migration. > > > > > > > > I had posted an RFC a while ago on the list: > > > > https://lists.gnu.org/archive/html/qemu-devel/2019-06/msg04924.html > > > > https://lists.gnu.org/archive/html/qemu-devel/2019-06/msg04923.html > > > > > > > > My mentors (Marcel and Yuval) told me to ask you for help > > > > regarding this. It would be really great if you can guide me in > > > > finding a workaround for this. > > > > > > Hi, > > > I'll have a look; I need to get some other things finished first. > > > > Adding cc: qemu-devel, sorry for the private email. > > I haven't looked deeply but it's surprising that you're hitting > BounceBuffer. My understanding is that's an old mechanism for > supporting exotic things like DMAing to/from device MMIO registers. > > Modern machines and guest software usually don't do this. I wonder why > you're hitting this case. > > If you look at the BounceBuffer code there's an API to register a > callback (cpu_register_map_client()). That's how the case of multiple > BounceBuffers is supposed to be handled. > > Can you double-check your code and figure out how it got here? I don't > think it should be taking this path. Looking at address_space_map I see it uses bounce buffers if !memory_access_is_direct, and that seems to be a check to see if the memory region is actually a normal block of RAM. Dave > Stefan -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
Re: [Qemu-devel] [GSoC] Help needed in implementing live migration
On Thu, Jun 27, 2019 at 05:02:33AM +0530, Sukrit Bhatnagar wrote: > On Tue, 25 Jun 2019 at 00:11, Dr. David Alan Gilbert > wrote: > > > > * Sukrit Bhatnagar (skrtbht...@gmail.com) wrote: > > > Hi David, > > > > > > I am Sukrit, GSoC participant working on PVRDMA live migration. > > > We had a short chat about vmxnet3 migration about a week ago > > > on the IRC channel. > > > > > > I am facing an issue while doing migration of the pvrdma device. > > > While loading the device state, we need to perform a few dma > > > mappings on the destination. But on the destination, the migration > > > fails due a BounceBuffer being locked (in_use). This global > > > BounceBuffer is used in address_space_map/unmap functions > > > which the rdma_pci_dma_map/unmap calls. > > > Essentially, we need a way to remap guest physical address on > > > the destination after migration. > > > > > > I had posted an RFC a while ago on the list: > > > https://lists.gnu.org/archive/html/qemu-devel/2019-06/msg04924.html > > > https://lists.gnu.org/archive/html/qemu-devel/2019-06/msg04923.html > > > > > > My mentors (Marcel and Yuval) told me to ask you for help > > > regarding this. It would be really great if you can guide me in > > > finding a workaround for this. > > > > Hi, > > I'll have a look; I need to get some other things finished first. > > Adding cc: qemu-devel, sorry for the private email. I haven't looked deeply but it's surprising that you're hitting BounceBuffer. My understanding is that's an old mechanism for supporting exotic things like DMAing to/from device MMIO registers. Modern machines and guest software usually don't do this. I wonder why you're hitting this case. If you look at the BounceBuffer code there's an API to register a callback (cpu_register_map_client()). That's how the case of multiple BounceBuffers is supposed to be handled. Can you double-check your code and figure out how it got here? I don't think it should be taking this path. Stefan signature.asc Description: PGP signature
Re: [Qemu-devel] [GSoC] Help needed in implementing live migration
On Tue, 25 Jun 2019 at 00:11, Dr. David Alan Gilbert wrote: > > * Sukrit Bhatnagar (skrtbht...@gmail.com) wrote: > > Hi David, > > > > I am Sukrit, GSoC participant working on PVRDMA live migration. > > We had a short chat about vmxnet3 migration about a week ago > > on the IRC channel. > > > > I am facing an issue while doing migration of the pvrdma device. > > While loading the device state, we need to perform a few dma > > mappings on the destination. But on the destination, the migration > > fails due a BounceBuffer being locked (in_use). This global > > BounceBuffer is used in address_space_map/unmap functions > > which the rdma_pci_dma_map/unmap calls. > > Essentially, we need a way to remap guest physical address on > > the destination after migration. > > > > I had posted an RFC a while ago on the list: > > https://lists.gnu.org/archive/html/qemu-devel/2019-06/msg04924.html > > https://lists.gnu.org/archive/html/qemu-devel/2019-06/msg04923.html > > > > My mentors (Marcel and Yuval) told me to ask you for help > > regarding this. It would be really great if you can guide me in > > finding a workaround for this. > > Hi, > I'll have a look; I need to get some other things finished first. Adding cc: qemu-devel, sorry for the private email. > Dave > > Thanks, > > Sukrit > -- > Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
