On Fri, May 21, 2021 at 07:58:57AM -0700, Rob Clark wrote:
On Fri, May 21, 2021 at 2:10 AM Daniel Vetter daniel.vetter@ffwll.ch wrote:
- msm is mildly entertaining. It also supports MSM_SUBMIT_NO_IMPLICIT, but because it doesn't use the drm/scheduler it handles fences from the wrong context with a synchronous dma_fence_wait. See submit_fence_sync() leading to msm_gem_sync_object(). Investing into a scheduler might be a good idea.
Yeah, drm/scheduler is (along with a lot of other things) on the TODO list. But this isn't quite as bad as it sounds because userspace uses a u_queue thread to call the submit ioctl rather than blocking the driver. (It also offloads some other work from the driver thread, like submit merging to reduce # of ioctls. Coincidentally that arrangement was a step towards preparing userspace for some hypothetical non-ioctl uapi ;-))
You're also holding a pile of locks, which I expect latest with multi-engine buffer sharing will be pain. If you push this to the scheduler then the locks aren't held. Or maybe I've misread the flow, it's become all a bit a blurr after all these drivers :-)
OTOH it would be good to move blocking until the system can free enough pages to repin bo's out of the ioctl path to better handle some memory pressure corner cases without having to be interruptable over a lot more of the submit path.. Running chrome+android on devices without a lot of memory is fun..
Uh that one needs the userspace thread. Or entirely different semantics of your ioctl, because you're not allowed to allocate memory once any dma_fence is visible. So offloading the entire pinning to a submit thread is no-go. -Daniel