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

[Tvrtko Ursulin]

On 11/07/2024 06:12, 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.
> 
> v2: Simplify can_preemt() function (Tvrtko Ursulin)

Yeah sorry for that yesterday when I thought gen8 emit bb was dead code, 
somehow I thought there was a gen9 emit_bb flavour. Looks like I 
confused it with something else.

> 
> 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+
> ---
>   .../drm/i915/gt/intel_execlists_submission.c    | 17 ++++++++---------
>   1 file changed, 8 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..59885d7721e4 100644
> --- a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> +++ b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> @@ -294,11 +294,19 @@ 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)
> +{
> +	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 (!can_preempt(engine))
> +		return false;
> +
>   	if (!intel_engine_has_semaphores(engine))

Patch looks clean now. Hmmm one new observation is whether the "has 
semaphores" check is now redundant? Looks preemption depends on 
semaphore support in logical_ring_default_vfuncs().

Regards,

Tvrtko

>   		return false;
>   
> @@ -3313,15 +3321,6 @@ 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;