drm/i915/gt: Defer schedule_out until after the next dequeue

Inside schedule_out, we do extra work upon idling the context, such as
updating the runtime, kicking off retires, kicking virtual engines.
However, if we are in a series of processing single requests per
contexts, we may find ourselves scheduling out the context, only to
immediately schedule it back in during dequeue. This is just extra work
that we can avoid if we keep the context marked as inflight across the
dequeue. This becomes more significant later on for minimising virtual
engine misses.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201224135544.1713-4-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/intel_context_types.h

@@ -58,8 +58,12 @@ struct intel_context {
 
 	struct intel_engine_cs *engine;
 	struct intel_engine_cs *inflight;
-#define intel_context_inflight(ce) ptr_mask_bits(READ_ONCE((ce)->inflight), 2)
-#define intel_context_inflight_count(ce) ptr_unmask_bits(READ_ONCE((ce)->inflight), 2)
+#define __intel_context_inflight(engine) ptr_mask_bits(engine, 3)
+#define __intel_context_inflight_count(engine) ptr_unmask_bits(engine, 3)
+#define intel_context_inflight(ce) \
+	__intel_context_inflight(READ_ONCE((ce)->inflight))
+#define intel_context_inflight_count(ce) \
+	__intel_context_inflight_count(READ_ONCE((ce)->inflight))
 
 	struct i915_address_space *vm;
 	struct i915_gem_context __rcu *gem_context;