Re: [PATCH RFC 00/12] vdpa: generalize vdpa simulator and add block device

[Stefano Garzarella]

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.

Yeah, maybe this is the case where virtio_ring and vringh use IOTLB 
concorrentetively.

> It might be useful to log the dma_map/unmp in both virtio_ring and 
> vringh to see who is missing the map.

I'll try.

Thanks for the hints,
Stefano