On Tue, Jul 22, 2014 at 09:28:51AM +0200, Daniel Vetter wrote: > On Mon, Jul 21, 2014 at 03:03:07PM -0400, Jerome Glisse wrote: > > On Mon, Jul 21, 2014 at 09:41:29PM +0300, Oded Gabbay wrote: > > > On 21/07/14 21:22, Daniel Vetter wrote: > > > > On Mon, Jul 21, 2014 at 7:28 PM, Oded Gabbay <oded.gabbay@xxxxxxx> wrote: > > > >>> I'm not sure whether we can do the same trick with the hw scheduler. But > > > >>> then unpinning hw contexts will drain the pipeline anyway, so I guess we > > > >>> can just stop feeding the hw scheduler until it runs dry. And then unpin > > > >>> and evict. > > > >> So, I'm afraid but we can't do this for AMD Kaveri because: > > > > > > > > Well as long as you can drain the hw scheduler queue (and you can do > > > > that, worst case you have to unmap all the doorbells and other stuff > > > > to intercept further submission from userspace) you can evict stuff. > > > > > > I can't drain the hw scheduler queue, as I can't do mid-wave preemption. > > > Moreover, if I use the dequeue request register to preempt a queue > > > during a dispatch it may be that some waves (wave groups actually) of > > > the dispatch have not yet been created, and when I reactivate the mqd, > > > they should be created but are not. However, this works fine if you use > > > the HIQ. the CP ucode correctly saves and restores the state of an > > > outstanding dispatch. I don't think we have access to the state from > > > software at all, so it's not a bug, it is "as designed". > > > > > > > I think here Daniel is suggesting to unmapp the doorbell page, and track > > each write made by userspace to it and while unmapped wait for the gpu to > > drain or use some kind of fence on a special queue. Once GPU is drain we > > can move pinned buffer, then remap the doorbell and update it to the last > > value written by userspace which will resume execution to the next job. > > Exactly, just prevent userspace from submitting more. And if you have > misbehaving userspace that submits too much, reset the gpu and tell it > that you're sorry but won't schedule any more work. > > We have this already in i915 (since like all other gpus we're not > preempting right now) and it works. There's some code floating around to > even restrict the reset to _just_ the offending submission context, with > nothing else getting corrupted. > > You can do all this with the doorbells and unmapping them, but it's a > pain. Much easier if you have a real ioctl, and I haven't seen anyone with > perf data indicating that an ioctl would be too much overhead on linux. > Neither in this thread nor internally here at intel. Aside: Another reason why the ioctl is better than the doorbell is integration with other drivers. Yeah I know this is about compute, but sooner or later someone will want to e.g. post-proc video frames between the v4l capture device and the gpu mpeg encoder. Or something else fancy. Then you want to be able to somehow integrate into a cross-driver fence framework like android syncpts, and you can't do that without an ioctl for the compute submissions. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>