1. 27 Sep, 2019 13 commits
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  5. 23 Sep, 2019 1 commit
    • Chris Wilson's avatar
      drm/i915: Prevent bonded requests from overtaking each other on preemption · e2144503
      Chris Wilson authored
      Force bonded requests to run on distinct engines so that they cannot be
      shuffled onto the same engine where timeslicing will reverse the order.
      A bonded request will often wait on a semaphore signaled by its master,
      creating an implicit dependency -- if we ignore that implicit dependency
      and allow the bonded request to run on the same engine and before its
      master, we will cause a GPU hang. [Whether it will hang the GPU is
      debatable, we should keep on timeslicing and each timeslice should be
      "accidentally" counted as forward progress, in which case it should run
      but at one-half to one-third speed.]
      
      We can prevent this inversion by restricting which engines we allow
      ourselves to jump to upon preemption, i.e. baking in the arrangement
      established at first execution. (We should also consider capturing the
      implicit dependency using i915_sched_add_dependency(), but first we need
      to think about the constraints that requires on the execution/retirement
      ordering.)
      
      Fixes: 8ee36e04 ("drm/i915/execlists: Minimalistic timeslicing")
      References: ee113690 ("drm/i915/execlists: Virtual engine bonding")
      Testcase: igt/gem_exec_balancer/bonded-slice
      Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
      Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
      Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
      Reviewed-by: default avatarTvrtko Ursulin <tvrtko.ursulin@intel.com>
      Link: https://patchwork.freedesktop.org/patch/msgid/20190923152844.8914-3-chris@chris-wilson.co.uk
      e2144503