On Thu, Mar 17, 2022 at 9:45 AM Christian König christian.koenig@amd.com wrote:
Am 17.03.22 um 17:18 schrieb Rob Clark:
On Thu, Mar 17, 2022 at 9:04 AM Christian König christian.koenig@amd.com wrote:
Am 17.03.22 um 16:10 schrieb Rob Clark:
[SNIP] userspace frozen != kthread frozen .. that is what this patch is trying to address, so we aren't racing between shutting down the hw and the scheduler shoveling more jobs at us.
Well exactly that's the problem. The scheduler is supposed to shoveling more jobs at us until it is empty.
Thinking more about it we will then keep some dma_fence instance unsignaled and that is and extremely bad idea since it can lead to deadlocks during suspend.
Hmm, perhaps that is true if you need to migrate things out of vram? It is at least not a problem when vram is not involved.
No, it's much wider than that.
See what can happen is that the memory management shrinkers want to wait for a dma_fence during suspend.
we don't wait on fences in shrinker, only purging or evicting things that are already ready. Actually, waiting on fences in shrinker path sounds like a pretty bad idea.
And if you stop the scheduler they will just wait forever.
What you need to do instead is to drain the scheduler, e.g. call drm_sched_entity_flush() with a proper timeout for each entity you have created.
yeah, it would work to drain the scheduler.. I guess that might be the more portable approach as far as generic solution for suspend.
BR, -R
Regards, Christian.
So this patch here is an absolute clear NAK from my side. If amdgpu is doing something similar that is a severe bug and needs to be addressed somehow.
I think amdgpu's use of kthread_park is not related to suspend, but didn't look too closely.
And perhaps the solution for this problem is more complex in the case of amdgpu, I'm not super familiar with the constraints there. But I think it is a fine solution for integrated GPUs.
BR, -R
Regards, Christian.
BR, -R