Re: [PATCH 18/39] drm/i915: Differentiate between ggtt->mutex and ppgtt->mutex

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> We have two classes of VM, global GTT and per-process GTT. In order to
> allow ourselves the freedom to mix both along call chains, distinguish
> the two classes with regards to their mutex and lockdep maps.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_gem_gtt.c       | 10 +++++-----
>  drivers/gpu/drm/i915/i915_gem_gtt.h       |  2 ++
>  drivers/gpu/drm/i915/selftests/mock_gtt.c |  6 +++---
>  3 files changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> index 852dbc1f185f..8f93b1dffbb9 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> @@ -474,8 +474,7 @@ static void vm_free_page(struct i915_address_space *vm, struct page *page)
>  	spin_unlock(&vm->free_pages.lock);
>  }
>  
> -static void i915_address_space_init(struct i915_address_space *vm,
> -				    struct drm_i915_private *dev_priv)
> +static void i915_address_space_init(struct i915_address_space *vm, int subclass)
>  {
>  	/*
>  	 * The vm->mutex must be reclaim safe (for use in the shrinker).
> @@ -483,6 +482,7 @@ static void i915_address_space_init(struct i915_address_space *vm,
>  	 * attempt holding the lock is immediately reported by lockdep.
>  	 */
>  	mutex_init(&vm->mutex);
> +	lockdep_set_subclass(&vm->mutex, subclass);

First I was confused as this is per instance. But yeah
lockdep tracks by class.

>  	i915_gem_shrinker_taints_mutex(&vm->mutex);
>  
>  	GEM_BUG_ON(!vm->total);
> @@ -1548,7 +1548,7 @@ static struct i915_hw_ppgtt *gen8_ppgtt_create(struct drm_i915_private *i915)
>  	/* From bdw, there is support for read-only pages in the PPGTT. */
>  	ppgtt->vm.has_read_only = true;
>  
> -	i915_address_space_init(&ppgtt->vm, i915);
> +	i915_address_space_init(&ppgtt->vm, VM_CLASS_PPGTT);
>  
>  	/* There are only few exceptions for gen >=6. chv and bxt.
>  	 * And we are not sure about the latter so play safe for now.
> @@ -1997,7 +1997,7 @@ static struct i915_hw_ppgtt *gen6_ppgtt_create(struct drm_i915_private *i915)
>  
>  	ppgtt->base.vm.total = I915_PDES * GEN6_PTES * I915_GTT_PAGE_SIZE;
>  
> -	i915_address_space_init(&ppgtt->base.vm, i915);
> +	i915_address_space_init(&ppgtt->base.vm, VM_CLASS_PPGTT);
>  
>  	ppgtt->base.vm.allocate_va_range = gen6_alloc_va_range;
>  	ppgtt->base.vm.clear_range = gen6_ppgtt_clear_range;
> @@ -3434,7 +3434,7 @@ int i915_ggtt_init_hw(struct drm_i915_private *dev_priv)
>  	 * and beyond the end of the GTT if we do not provide a guard.
>  	 */
>  	mutex_lock(&dev_priv->drm.struct_mutex);
> -	i915_address_space_init(&ggtt->vm, dev_priv);
> +	i915_address_space_init(&ggtt->vm, VM_CLASS_GGTT);
>  
>  	ggtt->vm.is_ggtt = true;
>  
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.h b/drivers/gpu/drm/i915/i915_gem_gtt.h
> index e2360f16427a..9229b03d629b 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.h
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.h
> @@ -288,6 +288,8 @@ struct i915_address_space {
>  	bool closed;
>  
>  	struct mutex mutex; /* protects vma and our lists */
> +#define VM_CLASS_GGTT 0
> +#define VM_CLASS_PPGTT 1
>  
>  	u64 scratch_pte;
>  	struct i915_page_dma scratch_page;
> diff --git a/drivers/gpu/drm/i915/selftests/mock_gtt.c b/drivers/gpu/drm/i915/selftests/mock_gtt.c
> index 6ae418c76015..976c862b3842 100644
> --- a/drivers/gpu/drm/i915/selftests/mock_gtt.c
> +++ b/drivers/gpu/drm/i915/selftests/mock_gtt.c
> @@ -70,7 +70,7 @@ mock_ppgtt(struct drm_i915_private *i915,
>  	ppgtt->vm.total = round_down(U64_MAX, PAGE_SIZE);
>  	ppgtt->vm.file = ERR_PTR(-ENODEV);
>  
> -	i915_address_space_init(&ppgtt->vm, i915);
> +	i915_address_space_init(&ppgtt->vm, VM_CLASS_PPGTT);
>  
>  	ppgtt->vm.clear_range = nop_clear_range;
>  	ppgtt->vm.insert_page = mock_insert_page;
> @@ -102,6 +102,7 @@ void mock_init_ggtt(struct drm_i915_private *i915)
>  	struct i915_ggtt *ggtt = &i915->ggtt;
>  
>  	ggtt->vm.i915 = i915;
> +	ggtt->vm.is_ggtt = true;

On the non mocking side we set this after the address space init,
so wrt that it is asymmetric.

>  
>  	ggtt->gmadr = (struct resource) DEFINE_RES_MEM(0, 2048 * PAGE_SIZE);
>  	ggtt->mappable_end = resource_size(&ggtt->gmadr);
> @@ -117,9 +118,8 @@ void mock_init_ggtt(struct drm_i915_private *i915)
>  	ggtt->vm.vma_ops.set_pages   = ggtt_set_pages;
>  	ggtt->vm.vma_ops.clear_pages = clear_pages;
>  
> -	i915_address_space_init(&ggtt->vm, i915);
>  
> -	ggtt->vm.is_ggtt = true;

Extra whitespace remains here.

> +	i915_address_space_init(&ggtt->vm, VM_CLASS_GGTT);

And now when you have the subclass, you could
embrace it fully and set the is_ggtt based on it,
inside i915_address_space_init.

-Mika

>  }
>  
>  void mock_fini_ggtt(struct drm_i915_private *i915)
> -- 
> 2.20.1
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