[PATCH v3] drm/i915/gt: Do not consider preemption during execlists_dequeue for gen8

[Cavitt, Jonathan]

-----Original Message-----
From: Intel-gfx <intel-gfx-bounces at lists.freedesktop.org> On Behalf Of Nitin Gote
Sent: Thursday, July 11, 2024 9:32 AM
To: Wilson, Chris P <chris.p.wilson at intel.com>; tursulin at ursulin.net; intel-gfx at lists.freedesktop.org
Cc: dri-devel at lists.freedesktop.org; Shyti, Andi <andi.shyti at intel.com>; Das, Nirmoy <nirmoy.das at intel.com>; janusz.krzysztofik at linux.intel.com; Gote, Nitin R <nitin.r.gote at intel.com>; Chris Wilson <chris.p.wilson at linux.intel.com>; stable at vger.kernel.org
Subject: [PATCH v3] drm/i915/gt: Do not consider preemption during execlists_dequeue for gen8
> 
> 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.

That seems to mean the original can_preempt function was inaccurately built,
so fixing it here makes the most sense to me, especially if it's causing problems.

Reviewed-by: Jonathan Cavitt <jonathan.cavitt at intel.com>
-Jonathan Cavitt

> So, add a fix to not consider preemption
> during dequeuing for gen8 platforms.
> 
> v2: Simplify can_preempt() function (Tvrtko Ursulin)
> 
> v3:
>  - Inside need_preempt(), condition of can_preempt() is not required
>    as simplified can_preempt() is enough. (Chris Wilson)
> 
> 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 at intel.com>
> Signed-off-by: Nitin Gote <nitin.r.gote at intel.com>
> Cc: Chris Wilson <chris.p.wilson at linux.intel.com>
> CC: <stable at vger.kernel.org> # v5.2+
> ---
>  drivers/gpu/drm/i915/gt/intel_execlists_submission.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 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..72090f52fb85 100644
> --- a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> +++ b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> @@ -3315,11 +3315,7 @@ static void remove_from_engine(struct i915_request *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;
> +	return GRAPHICS_VER(engine->i915) > 8;
>  }
>  
>  static void kick_execlists(const struct i915_request *rq, int prio)
> -- 
> 2.25.1
> 
>