Re: [PATCH] drm/i915/gt: Do not consider preemption during execlists_dequeue for gen8

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On 09/07/2024 15:02, Tvrtko Ursulin wrote:

On 09/07/2024 13:53, Nitin Gote wrote:
We're seeing a GPU HANG issue on a CHV platform, which was caused by
bac24f59f454 ("drm/i915/execlists: Enable coarse preemption boundaries for gen8").

Gen8 platform has only timeslice and doesn't support a preemption mechanism
as engines do not have a preemption timer and doesn't send an irq if the
preemption timeout expires. So, add a fix to not consider preemption
during dequeuing for gen8 platforms.

Also move can_preemt() above need_preempt() function to resolve implicit
declaration of function ‘can_preempt' error and make can_preempt()
function param as const to resolve error: passing argument 1 of
‘can_preempt’ discards ‘const’ qualifier from the pointer target type.

Fixes: bac24f59f454 ("drm/i915/execlists: Enable coarse preemption boundaries for gen8")
Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/11396
Suggested-by: Andi Shyti <andi.shyti@xxxxxxxxx>
Signed-off-by: Nitin Gote <nitin.r.gote@xxxxxxxxx>
Cc: Chris Wilson <chris.p.wilson@xxxxxxxxxxxxxxx>
CC: <stable@xxxxxxxxxxxxxxx> # v5.2+
---
  .../drm/i915/gt/intel_execlists_submission.c  | 24 ++++++++++++-------
  1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
index 21829439e686..30631cc690f2 100644
--- a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
+++ b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
@@ -294,11 +294,26 @@ static int virtual_prio(const struct intel_engine_execlists *el)
      return rb ? rb_entry(rb, struct ve_node, rb)->prio : INT_MIN;
  }
+static bool can_preempt(const struct intel_engine_cs *engine)
+{
+    if (GRAPHICS_VER(engine->i915) > 8)
+        return true;
+
+    if (IS_CHERRYVIEW(engine->i915) || IS_BROADWELL(engine->i915))
+        return false;
+
+    /* GPGPU on bdw requires extra w/a; not implemented */
+    return engine->class != RENDER_CLASS;

Aren't BDW and CHV the only Gen8 platforms, in which case this function can be simplifies as:

...
{
     return GRAPHICS_VER(engine->i915) > 8;
}

?

+}
+
  static bool need_preempt(const struct intel_engine_cs *engine,
               const struct i915_request *rq)
  {
      int last_prio;
+    if ((GRAPHICS_VER(engine->i915) <= 8) && can_preempt(engine))

The GRAPHICS_VER check here looks redundant with the one inside can_preempt().

One more thing - I think gen8_emit_bb_start() becomes dead code after this and can be removed.

Regards,

Tvrtko

+        return false;
+
      if (!intel_engine_has_semaphores(engine))
          return false;
@@ -3313,15 +3328,6 @@ static void remove_from_engine(struct i915_request *rq)
      i915_request_notify_execute_cb_imm(rq);
  }
-static bool can_preempt(struct intel_engine_cs *engine)
-{
-    if (GRAPHICS_VER(engine->i915) > 8)
-        return true;
-
-    /* GPGPU on bdw requires extra w/a; not implemented */
-    return engine->class != RENDER_CLASS;
-}
-
  static void kick_execlists(const struct i915_request *rq, int prio)
  {
      struct intel_engine_cs *engine = rq->engine;



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