drm/i915/gt: Only swap to a random sibling once upon creation (110f9efa) · Commits · 戴 / test

The danger in switching at random upon intel_context_pin is that the context may still actually be inflight, as it will not be scheduled out until a context switch after it is complete -- that may be a long time after we do a final intel_context_unpin. Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2118 Fixes: ("drm/i915: Load balancing across a virtual engine") Signed-off-by:

Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: <stable@vger.kernel.org> # v5.3+ Reviewed-by:

Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20200713160549.17344-1-chris@chris-wilson.co.uk (cherry picked from commit ) Signed-off-by:

Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/gt/intel_lrc.c

+4 −14

Original line number	Diff line number	Diff line
		@@ -5396,13 +5396,8 @@ static void virtual_engine_initial_hint(struct virtual_engine *ve)
		* typically be the first we inspect for submission.
		*/
		swp = prandom_u32_max(ve->num_siblings);
		if (!swp)
		return;

		if (swp)
		swap(ve->siblings[swp], ve->siblings[0]);
		if (!intel_engine_has_relative_mmio(ve->siblings[0]))
		virtual_update_register_offsets(ve->context.lrc_reg_state,
		ve->siblings[0]);
		}

		static int virtual_context_alloc(struct intel_context *ce)
		@@ -5415,15 +5410,9 @@ static int virtual_context_alloc(struct intel_context *ce)
		static int virtual_context_pin(struct intel_context *ce)
		{
		struct virtual_engine ve = container_of(ce, typeof(ve), context);
		int err;

		/* Note: we must use a real engine class for setting up reg state */
		err = __execlists_context_pin(ce, ve->siblings[0]);
		if (err)
		return err;

		virtual_engine_initial_hint(ve);
		return 0;
		return __execlists_context_pin(ce, ve->siblings[0]);
		}

		static void virtual_context_enter(struct intel_context *ce)
		@@ -5770,6 +5759,7 @@ intel_execlists_create_virtual(struct intel_engine_cs **siblings,

		ve->base.flags \|= I915_ENGINE_IS_VIRTUAL;

		virtual_engine_initial_hint(ve);
		return &ve->context;

		err_put:

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