On 13/07/2020 17:05, Chris Wilson wrote:

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 is after we do a final intel_context_unpin.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2118 Fixes: 6d06779e8672 ("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+

---

drivers/gpu/drm/i915/gt/intel_lrc.c | 18 ++++-------------- 1 file changed, 4 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c index cd4262cc96e2..f4658849b08a 100644 --- a/drivers/gpu/drm/i915/gt/intel_lrc.c +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c @@ -5435,13 +5435,8 @@ 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;
  

• 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]);
  

• if (swp)

• swap(ve->siblings[swp], ve->siblings[0]);
  

  }

static int virtual_context_alloc(struct intel_context *ce) @@ -5454,15 +5449,9 @@ 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) @@ -5808,6 +5797,7 @@ 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:

Reviewed-by: Tvrtko Ursulin tvrtko.ursulin@intel.com

Regards,

Tvrtko