On Mon, 2023-12-18 at 13:06 +0100, Eugenio Perez Martin wrote: > On Mon, Dec 18, 2023 at 11:52 AM Dragos Tatulea <dtatulea@xxxxxxxxxx> wrote: > > > > On Mon, 2023-12-18 at 11:16 +0100, Eugenio Perez Martin wrote: > > > On Sat, Dec 16, 2023 at 12:03 PM Dragos Tatulea <dtatulea@xxxxxxxxxx> wrote: > > > > > > > > On Fri, 2023-12-15 at 18:56 +0100, Eugenio Perez Martin wrote: > > > > > On Fri, Dec 15, 2023 at 3:13 PM Dragos Tatulea <dtatulea@xxxxxxxxxx> wrote: > > > > > > > > > > > > On Fri, 2023-12-15 at 12:35 +0000, Dragos Tatulea wrote: > > > > > > > On Thu, 2023-12-14 at 19:30 +0100, Eugenio Perez Martin wrote: > > > > > > > > On Thu, Dec 14, 2023 at 4:51 PM Dragos Tatulea <dtatulea@xxxxxxxxxx> wrote: > > > > > > > > > > > > > > > > > > On Thu, 2023-12-14 at 08:45 -0500, Michael S. Tsirkin wrote: > > > > > > > > > > On Thu, Dec 14, 2023 at 01:39:55PM +0000, Dragos Tatulea wrote: > > > > > > > > > > > On Tue, 2023-12-12 at 15:44 -0800, Si-Wei Liu wrote: > > > > > > > > > > > > > > > > > > > > > > > > On 12/12/2023 11:21 AM, Eugenio Perez Martin wrote: > > > > > > > > > > > > > On Tue, Dec 5, 2023 at 11:46 AM Dragos Tatulea <dtatulea@xxxxxxxxxx> wrote: > > > > > > > > > > > > > > Addresses get set by .set_vq_address. hw vq addresses will be updated on > > > > > > > > > > > > > > next modify_virtqueue. > > > > > > > > > > > > > > > > > > > > > > > > > > > > Signed-off-by: Dragos Tatulea <dtatulea@xxxxxxxxxx> > > > > > > > > > > > > > > Reviewed-by: Gal Pressman <gal@xxxxxxxxxx> > > > > > > > > > > > > > > Acked-by: Eugenio Pérez <eperezma@xxxxxxxxxx> > > > > > > > > > > > > > I'm kind of ok with this patch and the next one about state, but I > > > > > > > > > > > > > didn't ack them in the previous series. > > > > > > > > > > > > > > > > > > > > > > > > > > My main concern is that it is not valid to change the vq address after > > > > > > > > > > > > > DRIVER_OK in VirtIO, which vDPA follows. Only memory maps are ok to > > > > > > > > > > > > > change at this moment. I'm not sure about vq state in vDPA, but vhost > > > > > > > > > > > > > forbids changing it with an active backend. > > > > > > > > > > > > > > > > > > > > > > > > > > Suspend is not defined in VirtIO at this moment though, so maybe it is > > > > > > > > > > > > > ok to decide that all of these parameters may change during suspend. > > > > > > > > > > > > > Maybe the best thing is to protect this with a vDPA feature flag. > > > > > > > > > > > > I think protect with vDPA feature flag could work, while on the other > > > > > > > > > > > > hand vDPA means vendor specific optimization is possible around suspend > > > > > > > > > > > > and resume (in case it helps performance), which doesn't have to be > > > > > > > > > > > > backed by virtio spec. Same applies to vhost user backend features, > > > > > > > > > > > > variations there were not backed by spec either. Of course, we should > > > > > > > > > > > > try best to make the default behavior backward compatible with > > > > > > > > > > > > virtio-based backend, but that circles back to no suspend definition in > > > > > > > > > > > > the current virtio spec, for which I hope we don't cease development on > > > > > > > > > > > > vDPA indefinitely. After all, the virtio based vdap backend can well > > > > > > > > > > > > define its own feature flag to describe (minor difference in) the > > > > > > > > > > > > suspend behavior based on the later spec once it is formed in future. > > > > > > > > > > > > > > > > > > > > > > > So what is the way forward here? From what I understand the options are: > > > > > > > > > > > > > > > > > > > > > > 1) Add a vdpa feature flag for changing device properties while suspended. > > > > > > > > > > > > > > > > > > > > > > 2) Drop these 2 patches from the series for now. Not sure if this makes sense as > > > > > > > > > > > this. But then Si-Wei's qemu device suspend/resume poc [0] that exercises this > > > > > > > > > > > code won't work anymore. This means the series would be less well tested. > > > > > > > > > > > > > > > > > > > > > > Are there other possible options? What do you think? > > > > > > > > > > > > > > > > > > > > > > [0] https://github.com/siwliu-kernel/qemu/tree/svq-resume-wip > > > > > > > > > > > > > > > > > > > > I am fine with either of these. > > > > > > > > > > > > > > > > > > > How about allowing the change only under the following conditions: > > > > > > > > > vhost_vdpa_can_suspend && vhost_vdpa_can_resume && > > > > > > > > > VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK is set > > > > > > > > > > > > > > > > > > ? > > > > > > > > > > > > > > > > I think the best option by far is 1, as there is no hint in the > > > > > > > > combination of these 3 indicating that you can change device > > > > > > > > properties in the suspended state. > > > > > > > > > > > > > > > Sure. Will respin a v3 without these two patches. > > > > > > > > > > > > > > Another series can implement option 2 and add these 2 patches on top. > > > > > > Hmm...I misunderstood your statement and sent a erroneus v3. You said that > > > > > > having a feature flag is the best option. > > > > > > > > > > > > Will add a feature flag in v4: is this similar to the > > > > > > VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK flag? > > > > > > > > > > > > > > > > Right, it should be easy to return it from .get_backend_features op if > > > > > the FW returns that capability, isn't it? > > > > > > > > > Yes, that's easy. But I wonder if we need one feature bit for each type of > > > > change: > > > > - VHOST_BACKEND_F_CHANGEABLE_VQ_ADDR_IN_SUSPEND > > > > - VHOST_BACKEND_F_CHANGEABLE_VQ_STATE_IN_SUSPEND > > > > > > > > > > I'd say yes. Although we could configure SVQ initial state in userland > > > as different than 0 for this first step, it would be needed in the > > > long term. > > > > > > > Or would a big one VHOST_BACKEND_F_CAN_RECONFIG_VQ_IN_SUSPEND suffice? > > > > > > > > > > I'd say "reconfig vq" is not valid as mlx driver doesn't allow > > > changing queue sizes, for example, isn't it? > > > > > Modifying the queue size for a vq is indeed not supported by the mlx device. > > > > > To define that it is > > > valid to change "all parameters" seems very confident. > > > > > Ack > > > > > > To me having individual feature bits makes sense. But it could also takes too > > > > many bits if more changes are required. > > > > > > > > > > Yes, that's a good point. Maybe it is valid to define a subset of > > > features that can be changed., but I think it is way clearer to just > > > check for individual feature bits. > > > > > I will prepare extra patches with the 2 feature bits approach. > > > > Is it necessary to add checks in the vdpa core that block changing these > > properties if the state is driver ok and the device doesn't support the feature? > > > > Yes, I think it is better to protect for changes in vdpa core. > Hmmm... there is no suspended state available. I would only add checks for the DRIVER_OK state of the device because adding a is_suspended state/op seems out of scope for this series. Any thoughts?
