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  1. Jun 15, 2019
    • Chris Wilson's avatar
      drm/i915: Keep contexts pinned until after the next kernel context switch · ce476c80
      Chris Wilson authored
      
      
      We need to keep the context image pinned in memory until after the GPU
      has finished writing into it. Since it continues to write as we signal
      the final breadcrumb, we need to keep it pinned until the request after
      it is complete. Currently we know the order in which requests execute on
      each engine, and so to remove that presumption we need to identify a
      request/context-switch we know must occur after our completion. Any
      request queued after the signal must imply a context switch, for
      simplicity we use a fresh request from the kernel context.
      
      The sequence of operations for keeping the context pinned until saved is:
      
       - On context activation, we preallocate a node for each physical engine
         the context may operate on. This is to avoid allocations during
         unpinning, which may be from inside FS_RECLAIM context (aka the
         shrinker)
      
       - On context deactivation on retirement of the last active request (which
         is before we know the context has been saved), we add the
         preallocated node onto a barrier list on each engine
      
       - On engine idling, we emit a switch to kernel context. When this
         switch completes, we know that all previous contexts must have been
         saved, and so on retiring this request we can finally unpin all the
         contexts that were marked as deactivated prior to the switch.
      
      We can enhance this in future by flushing all the idle contexts on a
      regular heartbeat pulse of a switch to kernel context, which will also
      be used to check for hung engines.
      
      v2: intel_context_active_acquire/_release
      
      Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
      Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
      Reviewed-by: default avatarMika Kuoppala <mika.kuoppala@linux.intel.com>
      Link: https://patchwork.freedesktop.org/patch/msgid/20190614164606.15633-1-chris@chris-wilson.co.uk
      ce476c80
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