Re: [Intel-gfx] [PATCH 4/5] drm/i915/gem: Pin gen6_ppgtt prior to constructing the request

[Andi Shyti <andi@etezian.org>]

Hi Chris,

> All pinning must be done prior to i915_request_create, to avoid
> timeline->mutex inversions.
> 
> Here we slightly abuse the context_barrier_task stages to utilise the
> 'skip' decision as an opportunity to acquire the pin on the new ppgtt.
> Consider it s/skip/prepare/. At the moment, we only have on user of
> context_barrier_task, so it might be worth breaking it down for the
> specific task of set-vm and refactor it later if we find a second
> purpose.

[...]

> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> index 9f1dc96b10a6..9d8d75765ee4 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> @@ -1141,8 +1141,6 @@ static int emit_ppgtt_update(struct i915_request *rq, void *data)
>  		*cs++ = MI_NOOP;
>  		intel_ring_advance(rq, cs);
>  	} else {
> -		/* ppGTT is not part of the legacy context image */
> -		gen6_ppgtt_pin(i915_vm_to_ppgtt(vm));
>  	}

mh? Am I not seeing something obvious? Can we remove the else?

>  
>  	return 0;
> @@ -1150,10 +1148,20 @@ static int emit_ppgtt_update(struct i915_request *rq, void *data)
>  
>  static bool skip_ppgtt_update(struct intel_context *ce, void *data)
>  {
> +	if (!test_bit(CONTEXT_ALLOC_BIT, &ce->flags))
> +		return true;
> +
>  	if (HAS_LOGICAL_RING_CONTEXTS(ce->engine->i915))
> -		return !ce->state;
> -	else
> -		return !atomic_read(&ce->pin_count);
> +		return false;
> +
> +	if (!atomic_read(&ce->pin_count))
> +		return true;
> +
> +	/* ppGTT is not part of the legacy context image */
> +	if (gen6_ppgtt_pin(i915_vm_to_ppgtt(ce->vm)))
> +		return true;
> +
> +	return false;

looks correct, a bit tricky, but I don't see any issue.

Reviewed-by: Andi Shyti <andi.shyti@intel.com>

Andi
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