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@xxxxxxxx> 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 -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
