Re: [Intel-gfx] [PATCH 16/66] drm/i915/gem: Remove the call for no-evict i915_vma_pin

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 15/07/2020 12:50, Chris Wilson wrote:
> Remove the stub i915_vma_pin() used for incrementally pining objects for
> execbuf (under the severe restriction that they must not wait on a
> resource as we may have already pinned it) and replace it with a
> i915_vma_pin_inplace() that is only allowed to reclaim the currently
> bound location for the vma (and will never wait for a pinned resource).
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>   .../gpu/drm/i915/gem/i915_gem_execbuffer.c    | 69 +++++++++++--------
>   drivers/gpu/drm/i915/i915_vma.c               |  6 +-
>   drivers/gpu/drm/i915/i915_vma.h               |  2 +
>   3 files changed, 45 insertions(+), 32 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> index 28cf28fcf80a..0b8a26da26e5 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> @@ -452,49 +452,55 @@ static u64 eb_pin_flags(const struct drm_i915_gem_exec_object2 *entry,
>   	return pin_flags;
>   }
>   
> +static bool eb_pin_vma_fence_inplace(struct eb_vma *ev)
> +{
> +	struct i915_vma *vma = ev->vma;
> +	struct i915_fence_reg *reg = vma->fence;
> +
> +	if (reg) {
> +		if (READ_ONCE(reg->dirty))
> +			return false;
> +
> +		atomic_inc(&reg->pin_count);

Why is this safe outside the vm->mutex? It otherwise seems to be 
protecting this pin count.

Regards,

Tvrtko

> +		ev->flags |= __EXEC_OBJECT_HAS_FENCE;
> +	} else {
> +		if (i915_gem_object_is_tiled(vma->obj))
> +			return false;
> +	}
> +
> +	return true;
> +}
> +
>   static inline bool
> -eb_pin_vma(struct i915_execbuffer *eb,
> -	   const struct drm_i915_gem_exec_object2 *entry,
> -	   struct eb_vma *ev)
> +eb_pin_vma_inplace(struct i915_execbuffer *eb,
> +		   const struct drm_i915_gem_exec_object2 *entry,
> +		   struct eb_vma *ev)
>   {
>   	struct i915_vma *vma = ev->vma;
> -	u64 pin_flags;
> +	unsigned int pin_flags;
>   
> -	if (vma->node.size)
> -		pin_flags = vma->node.start;
> -	else
> -		pin_flags = entry->offset & PIN_OFFSET_MASK;
> +	if (eb_vma_misplaced(entry, vma, ev->flags))
> +		return false;
>   
> -	pin_flags |= PIN_USER | PIN_NOEVICT | PIN_OFFSET_FIXED;
> +	pin_flags = PIN_USER;
>   	if (unlikely(ev->flags & EXEC_OBJECT_NEEDS_GTT))
>   		pin_flags |= PIN_GLOBAL;
>   
>   	/* Attempt to reuse the current location if available */
> -	if (unlikely(i915_vma_pin(vma, 0, 0, pin_flags))) {
> -		if (entry->flags & EXEC_OBJECT_PINNED)
> -			return false;
> -
> -		/* Failing that pick any _free_ space if suitable */
> -		if (unlikely(i915_vma_pin(vma,
> -					  entry->pad_to_size,
> -					  entry->alignment,
> -					  eb_pin_flags(entry, ev->flags) |
> -					  PIN_USER | PIN_NOEVICT)))
> -			return false;
> -	}
> +	if (!i915_vma_pin_inplace(vma, pin_flags))
> +		return false;
>   
>   	if (unlikely(ev->flags & EXEC_OBJECT_NEEDS_FENCE)) {
> -		if (unlikely(i915_vma_pin_fence(vma))) {
> -			i915_vma_unpin(vma);
> +		if (!eb_pin_vma_fence_inplace(ev)) {
> +			__i915_vma_unpin(vma);
>   			return false;
>   		}
> -
> -		if (vma->fence)
> -			ev->flags |= __EXEC_OBJECT_HAS_FENCE;
>   	}
>   
> +	GEM_BUG_ON(eb_vma_misplaced(entry, vma, ev->flags));
> +
>   	ev->flags |= __EXEC_OBJECT_HAS_PIN;
> -	return !eb_vma_misplaced(entry, vma, ev->flags);
> +	return true;
>   }
>   
>   static int
> @@ -676,14 +682,17 @@ static int eb_reserve_vm(struct i915_execbuffer *eb)
>   		struct drm_i915_gem_exec_object2 *entry = ev->exec;
>   		struct i915_vma *vma = ev->vma;
>   
> -		if (eb_pin_vma(eb, entry, ev)) {
> +		if (eb_pin_vma_inplace(eb, entry, ev)) {
>   			if (entry->offset != vma->node.start) {
>   				entry->offset = vma->node.start | UPDATE;
>   				eb->args->flags |= __EXEC_HAS_RELOC;
>   			}
>   		} else {
> -			eb_unreserve_vma(ev);
> -			list_add_tail(&ev->unbound_link, &unbound);
> +			/* Lightly sort user placed objects to the fore */
> +			if (ev->flags & EXEC_OBJECT_PINNED)
> +				list_add(&ev->unbound_link, &unbound);
> +			else
> +				list_add_tail(&ev->unbound_link, &unbound);
>   		}
>   	}
>   
> diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
> index c6bf04ca2032..dbe11b349175 100644
> --- a/drivers/gpu/drm/i915/i915_vma.c
> +++ b/drivers/gpu/drm/i915/i915_vma.c
> @@ -740,11 +740,13 @@ i915_vma_detach(struct i915_vma *vma)
>   	list_del(&vma->vm_link);
>   }
>   
> -static bool try_qad_pin(struct i915_vma *vma, unsigned int flags)
> +bool i915_vma_pin_inplace(struct i915_vma *vma, unsigned int flags)
>   {
>   	unsigned int bound;
>   	bool pinned = true;
>   
> +	GEM_BUG_ON(flags & ~I915_VMA_BIND_MASK);
> +
>   	bound = atomic_read(&vma->flags);
>   	do {
>   		if (unlikely(flags & ~bound))
> @@ -865,7 +867,7 @@ int i915_vma_pin(struct i915_vma *vma, u64 size, u64 alignment, u64 flags)
>   	GEM_BUG_ON(!(flags & (PIN_USER | PIN_GLOBAL)));
>   
>   	/* First try and grab the pin without rebinding the vma */
> -	if (try_qad_pin(vma, flags & I915_VMA_BIND_MASK))
> +	if (i915_vma_pin_inplace(vma, flags & I915_VMA_BIND_MASK))
>   		return 0;
>   
>   	err = vma_get_pages(vma);
> diff --git a/drivers/gpu/drm/i915/i915_vma.h b/drivers/gpu/drm/i915/i915_vma.h
> index d0d01f909548..03fea54fd573 100644
> --- a/drivers/gpu/drm/i915/i915_vma.h
> +++ b/drivers/gpu/drm/i915/i915_vma.h
> @@ -236,6 +236,8 @@ static inline void i915_vma_unlock(struct i915_vma *vma)
>   	dma_resv_unlock(vma->resv);
>   }
>   
> +bool i915_vma_pin_inplace(struct i915_vma *vma, unsigned int flags);
> +
>   int __must_check
>   i915_vma_pin(struct i915_vma *vma, u64 size, u64 alignment, u64 flags);
>   int i915_ggtt_pin(struct i915_vma *vma, u32 align, unsigned int flags);
> 
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