Messages in this thread | | | Subject | Re: [PATCH RFC 00/12] vdpa: generalize vdpa simulator and add block device | From | Jason Wang <> | Date | Tue, 22 Dec 2020 20:56:16 +0800 |
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On 2020/12/22 下午8:29, Jason Wang wrote: > > On 2020/12/22 下午6:57, Stefano Garzarella wrote: >> On Tue, Dec 22, 2020 at 10:44:48AM +0800, Jason Wang wrote: >>> >>> On 2020/12/21 下午7:14, Stefano Garzarella wrote: >>>> On Mon, Dec 21, 2020 at 11:16:54AM +0800, Jason Wang wrote: >>>>> >>>>> On 2020/12/18 下午7:38, Stefano Garzarella wrote: >>>>>> On Mon, Nov 16, 2020 at 11:37:48AM +0800, Jason Wang wrote: >>>>>>> >>>>>>> On 2020/11/13 下午9:47, Stefano Garzarella wrote: >>>>>>>> Thanks to Max that started this work! >>>>>>>> I took his patches, and extended the block simulator a bit. >>>>>>>> >>>>>>>> This series moves the network device simulator in a new module >>>>>>>> (vdpa_sim_net) and leaves the generic functions in the vdpa_sim >>>>>>>> core >>>>>>>> module, allowing the possibility to add new vDPA device >>>>>>>> simulators. >>>>>>>> Then we added a new vdpa_sim_blk module to simulate a block >>>>>>>> device. >>>>>>>> >>>>>>>> I'm not sure about patch 11 ("vringh: allow vringh_iov_xfer() >>>>>>>> to skip >>>>>>>> bytes when ptr is NULL"), maybe we can add a new functions >>>>>>>> instead of >>>>>>>> modify vringh_iov_xfer(). >>>>>>>> >>>>>>>> As Max reported, I'm also seeing errors with vdpa_sim_blk >>>>>>>> related to >>>>>>>> iotlb and vringh when there is high load, these are some of the >>>>>>>> error >>>>>>>> messages I can see randomly: >>>>>>>> >>>>>>>> vringh: Failed to access avail idx at 00000000e8deb2cc >>>>>>>> vringh: Failed to read head: idx 6289 address 00000000e1ad1d50 >>>>>>>> vringh: Failed to get flags at 000000006635d7a3 >>>>>>>> >>>>>>>> virtio_vdpa vdpa0: vringh_iov_push_iotlb() error: -14 offset: >>>>>>>> 0x2840000 len: 0x20000 >>>>>>>> virtio_vdpa vdpa0: vringh_iov_pull_iotlb() error: -14 offset: >>>>>>>> 0x58ee000 len: 0x3000 >>>>>>>> >>>>>>>> These errors should all be related to the fact that >>>>>>>> iotlb_translate() >>>>>>>> fails with -EINVAL, so it seems that we miss some mapping. >>>>>>> >>>>>>> >>>>>>> Is this only reproducible when there's multiple co-current >>>>>>> accessing of IOTLB? If yes, it's probably a hint that some kind >>>>>>> of synchronization is still missed somewhere. >>>>>>> >>>>>>> It might be useful to log the dma_map/unmp in both virtio_ring >>>>>>> and vringh to see who is missing the map. >>>>>>> >>>>>> >>>>>> Just an update about these issues with vdpa-sim-blk. >>>>>> I've been focusing a little bit on these failures over the last >>>>>> few days and have found two issues related to the IOTLB/IOMMU: >>>>>> >>>>>> 1. Some requests coming from the block layer fills the SG list >>>>>> with multiple buffers that had the same physical address. This >>>>>> happens for example while using 'mkfs', at some points multiple >>>>>> sectors are zeroed so multiple SG elements point to the same >>>>>> physical page that is zeroed. >>>>>> Since we are using vhost_iotlb_del_range() in the >>>>>> vdpasim_unmap_page(), this removes all the overlapped ranges. I >>>>>> fixed removing a single map in vdpasim_unmap_page(), but has an >>>>>> alternative we can implement some kind of reference counts. >>>>> >>>>> >>>>> I think we need to do what hardware do. So using refcount is >>>>> probably not a good ida. >>>> >>>> Okay, so since we are using for simplicity an identical mapping, we >>>> are assigning the same dma_addr to multiple pages. >>> >>> >>> I think I get you now. That's the root cause for the failure. >> >> Yes, sorry, I didn't explain well previously. >> >>> >>> Then I think we need an simple iova allocator for vdpa simulator, >>> and it might be useful for VDUSE as well. >> >> Okay, I'll work on it. >> If you have an example to follow or some pointers, they are welcome :-) > > > Kernel had implemented one in iova.c but I'm not sure we need the > complexity like that. Or we can just use rbtree or idr to implement a > simpler one.
VDUSE[1] implements another allocator, but it's still complicated since it needs to track bounce pages. I feel like we'd better start from a simple one.
Thanks
[1] https://www.spinics.net/lists/linux-mm/msg231576.html
> > Thanks > > >> >> Thanks, >> Stefano >>
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