Hi Daniel, May I know what's the requirement for adding render node support to a "gpu"? Why we just export render node for every drm devices? I read document here https://www.kernel.org/doc/html/v4.8/gpu/drm-uapi.html#render-nodes and it seems render node allow multiple unprivileged clients to work with the same gpu, I am not sure why we just enable it for all kms-only device. What's wrong if we enable it for all kms-only devices and also let mesa to use llvmpipe with those devices by default. Thanks! On Thu, Jan 5, 2023 at 7:35 AM Daniel Vetter <daniel@xxxxxxxx> wrote: > > On Fri, Jan 06, 2023 at 12:16:07AM +0900, Yi Xie wrote: > > On Thu, Jan 5, 2023 at 11:16 PM Daniel Vetter <daniel@xxxxxxxx> wrote: > > > > > > On Thu, Jan 05, 2023 at 11:10:23PM +0900, Yi Xie wrote: > > > > On Thu, Jan 5, 2023 at 10:48 PM Daniel Vetter <daniel@xxxxxxxx> wrote: > > > > > > > > > > On Thu, Jan 05, 2023 at 09:52:26PM +0900, Yi Xie wrote: > > > > > > > This doesn't sound like a good idea to me. Devices without render > > > > > > > capabilities should not fake it. > > > > > > > > > > > > > > User-space (e.g. wlroots) relies on "no render node" to enable > > > > > > > software rendering (Pixman instead of GL). > > > > > > > > > > > > We have virtgpu driver that exports a render node even when virgl is > > > > > > not supported. > > > > > > Mesa has special code path to enable software rendering on it: > > > > > > https://gitlab.freedesktop.org/mesa/mesa/-/blob/main/src/egl/drivers/dri2/platform_device.c#L296 > > > > > > We can do the same for vkms to force software rendering. > > > > > > > > > > Yeah that is the old kmsro mesa issue, for every combination of kms and > > > > > gem device you need one to make this work. > > > > > > > > > > > On Thu, Jan 5, 2023 at 8:36 PM Daniel Vetter <daniel@xxxxxxxx> wrote: > > > > > > > > > > > > > > On Thu, Jan 05, 2023 at 02:23:25PM +0900, Yi Xie wrote: > > > > > > > > Some libraries including Mesa and virglrenderer require a render node to > > > > > > > > fully function. By adding a render node to vkms those libraries will > > > > > > > > work properly, supporting use cases like running crosvm with virgl GPU > > > > > > > > support via llvmpipe on a headless virtual machine. > > > > > > > > > > > > > > This is what vgem exists for. More or less at least ... I'm honestly not > > > > > > > really understanding what you're trying to fix here, it sounds a bit like > > > > > > > userspace being stupid. > > > > > > > -Daniel > > > > > > The problem with vgem is that it crashes llvmpipe while working with vkms. > > > > > > Looks like it's due to the same reason as described in this thread in Mesa: > > > > > > https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5830 > > > > > > > > > > I'm not finding any bug description in there and how/why something > > > > > crashes? > > > > > > > > The discussion is in the comment section under the first comment by > > > > Emil Velikov. > > > > It's folded by default (inside "6 replies" at the bottom). > > > > > > > > > > > > > > > Importing buffers allocated by vgem to vkms seems to be unexpected and > > > > > > causes the crash. If we create a render node on vkms then llvmpipe will use > > > > > > vkms to allocate buffers and it no longer crashes. > > > > > > > > > > Uh importing vgem into virtio might not work because those sometimes need > > > > > special buffers iirc. But importing vgem into vkms really should work, > > > > > there's no technical reason it cannot. If it doesn't, then the right fix > > > > > would be to fix that, not paper around it. > > > > > > > > The crash stack trace looks like this: > > > > https://gist.github.com/imxieyi/03053ae79cee2e614850fd41829e1da2 > > > > > > > > Even if we fix the crash issue with vgem, we still need to workaround > > > > quite a few > > > > places that has explicitly blocked vgem. A notable example is virglrenderer: > > > > https://gitlab.freedesktop.org/virgl/virglrenderer/-/blob/master/src/vrend_winsys_gbm.c#L121 > > > > > > > > Actually I have tried to force running virglrenderer on vgem and it > > > > didn't work. I > > > > didn't look into why it wasn't working but I guess that's the reason > > > > for blocking > > > > vgem in the first place. Virglrenderer works well on vkms with render node > > > > enabled though. > > > > > > Ah ok. For next time around, copy a link to the comment you want, e.g. > > > > > > https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5830#note_582477 > > > > > > The 3 dots menu on each comments has an option to copy that link tag. That > > > also highlights the right comment. > > > > Thanks for the tips! Actually you need to sign in to reveal that 3 dots menu. > > > > > > > > On this issue, I'm concurring with Emil: > > > > > > "- the import is broken > > > "IMHO that should be fixed, regardless of the rest" > > > > > > The same should be done here. Unless it's a very special device, we should > > > be able to import vgem buffers. > > > > How about the fact that vgem is blocked explicitly in virglrenderer? > > We will have > > to remove it from block list and that may break something that > > resulted in blocking > > in this commit: > > https://gitlab.freedesktop.org/virgl/virglrenderer/-/commit/2cb686dd46df27e9600f9df734303ec57bb38772 > > I can't find the reason why it's blocking vgem though. It shouldn't be > > related to > > incompatibility with vkms/virtgpu. > > > > Are there any concerns that enabling render node on vkms may cause problems? > > What if we add a driver option to add render node on demand? > > The thing is, that none of the other kms-only driver enable render nodes. > If we start adding them in one case just because userspace can't cope, > then we'll have an endless stream of these patches. > > Instead of fixing userspace. > > Note that the issue is very old for at least mesa3d, and the only fix is > kmsro, where you have to build a driver for each combo. Maybe this should > be done better, dunno. But adding render node in just vkms for this use > case really doesn't make much sense to me, and it smells very much like > opening a can of worms :-/ > -Daniel > > > > -Daniel > > > > > > > > > > > > -Daniel > > > > > > > > > > > > > > > > > > > > > > > > > > > Signed-off-by: Yi Xie <yixie@xxxxxxxxxx> > > > > > > > > --- > > > > > > > > drivers/gpu/drm/vkms/vkms_drv.c | 2 +- > > > > > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > > > > > > > > > diff --git a/drivers/gpu/drm/vkms/vkms_drv.c b/drivers/gpu/drm/vkms/vkms_drv.c > > > > > > > > index 293dbca50c31..8eea5d4dece8 100644 > > > > > > > > --- a/drivers/gpu/drm/vkms/vkms_drv.c > > > > > > > > +++ b/drivers/gpu/drm/vkms/vkms_drv.c > > > > > > > > @@ -113,7 +113,7 @@ static void vkms_config_debugfs_init(struct drm_minor *minor) > > > > > > > > } > > > > > > > > > > > > > > > > static const struct drm_driver vkms_driver = { > > > > > > > > - .driver_features = DRIVER_MODESET | DRIVER_ATOMIC | DRIVER_GEM, > > > > > > > > + .driver_features = DRIVER_MODESET | DRIVER_ATOMIC | DRIVER_GEM | DRIVER_RENDER, > > > > > > > > .release = vkms_release, > > > > > > > > .fops = &vkms_driver_fops, > > > > > > > > DRM_GEM_SHMEM_DRIVER_OPS, > > > > > > > > -- > > > > > > > > 2.39.0.314.g84b9a713c41-goog > > > > > > > > > > > > > > > > > > > > > > -- > > > > > > > Daniel Vetter > > > > > > > Software Engineer, Intel Corporation > > > > > > > http://blog.ffwll.ch > > > > > > > > > > -- > > > > > Daniel Vetter > > > > > Software Engineer, Intel Corporation > > > > > http://blog.ffwll.ch > > > > > > -- > > > Daniel Vetter > > > Software Engineer, Intel Corporation > > > http://blog.ffwll.ch > > -- > Daniel Vetter > Software Engineer, Intel Corporation > http://blog.ffwll.ch
