Depending on contraints around preemption (ie. on what boundaries can
the GPU preempt) and priority of other processes using the GPU, the
compositor can get starved behind a long-running job.

This can be handled by a hangcheck timer that kills jobs that run too
long, but then there is a conflict between legit long running jobs
(opencl) and UI responsiveness.

This series adds a new sysrq key handler (SysRq-G because SysRq-g was
already taken) that kills the current job running on the GPU.  So a
longer hangcheck timer could be used but the user could still reclaim
their "hung" desktop by using SysRq-G to kill the background GPU job.

Sending this out as RFC to see what others think of the idea.  Possibly
the driver implementation should check how long the job has been
running to make sure it is only killing a long running job.  Possibly
we should kill the process behind the long running job, or at least
mark the context as unusable to prevent it from spamming more long
running jobs.  Etc.

Rob Clark (2):
  drm: Add sysrq key to kill current job on GPU
  drm/msm: Add sysrq_kill handler

 drivers/gpu/drm/Makefile        |  1 +
 drivers/gpu/drm/drm_dev_sysrq.c | 67 +++++++++++++++++++++++++++++++++
 drivers/gpu/drm/drm_drv.c       |  3 ++
 drivers/gpu/drm/drm_internal.h  | 11 ++++++
 drivers/gpu/drm/msm/msm_drv.c   | 12 ++++++
 drivers/gpu/drm/msm/msm_gpu.c   | 18 +++++++++
 drivers/gpu/drm/msm/msm_gpu.h   |  1 +
 include/drm/drm_device.h        |  8 ++++
 include/drm/drm_drv.h           |  7 ++++
 9 files changed, 128 insertions(+)
 create mode 100644 drivers/gpu/drm/drm_dev_sysrq.c

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2.53.0