Re: [PATCH v3 7/8] drm/panfrost: Implement generic DRM object RSS reporting function

[Boris Brezillon <boris.brezillon@collabora.com>]

On Tue,  5 Sep 2023 19:45:23 +0100
Adrián Larumbe <adrian.larumbe@collabora.com> wrote:

> BO's RSS is updated every time new pages are allocated on demand and mapped
> for the object at GPU page fault's IRQ handler, but only for heap buffers.
> The reason this is unnecessary for non-heap buffers is that they are mapped
> onto the GPU's VA space and backed by physical memory in their entirety at
> BO creation time.
> 
> This calculation is unnecessary for imported PRIME objects, since heap
> buffers cannot be exported by our driver, and the actual BO RSS size is the
> one reported in its attached dmabuf structure.
> 
> Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
> ---
>  drivers/gpu/drm/panfrost/panfrost_gem.c | 14 ++++++++++++++
>  drivers/gpu/drm/panfrost/panfrost_gem.h |  5 +++++
>  drivers/gpu/drm/panfrost/panfrost_mmu.c | 12 ++++++++----
>  3 files changed, 27 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c
> index 7d8f83d20539..cb92c0ed7615 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gem.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.c
> @@ -208,6 +208,19 @@ static enum drm_gem_object_status panfrost_gem_status(struct drm_gem_object *obj
>  	return res;
>  }
>  
> +static size_t panfrost_gem_rss(struct drm_gem_object *obj)
> +{
> +	struct panfrost_gem_object *bo = to_panfrost_bo(obj);
> +
> +	if (bo->is_heap)
> +		return bo->heap_rss_size;
> +	else if (bo->base.pages) {
> +		WARN_ON(bo->heap_rss_size);
> +		return bo->base.base.size;
> +	} else
> +		return 0;

Nit: please add brackets on all conditional blocks, even if only the
second one needs it.

> +}
> +
>  static const struct drm_gem_object_funcs panfrost_gem_funcs = {
>  	.free = panfrost_gem_free_object,
>  	.open = panfrost_gem_open,
> @@ -220,6 +233,7 @@ static const struct drm_gem_object_funcs panfrost_gem_funcs = {
>  	.vunmap = drm_gem_shmem_object_vunmap,
>  	.mmap = drm_gem_shmem_object_mmap,
>  	.status = panfrost_gem_status,
> +	.rss = panfrost_gem_rss,
>  	.vm_ops = &drm_gem_shmem_vm_ops,
>  };
>  
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.h b/drivers/gpu/drm/panfrost/panfrost_gem.h
> index ad2877eeeccd..13c0a8149c3a 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gem.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.h
> @@ -36,6 +36,11 @@ struct panfrost_gem_object {
>  	 */
>  	atomic_t gpu_usecount;
>  
> +	/*
> +	 * Object chunk size currently mapped onto physical memory
> +	 */
> +	size_t heap_rss_size;
> +
>  	bool noexec		:1;
>  	bool is_heap		:1;
>  };
> diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> index d54d4e7b2195..67c206124781 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> @@ -285,17 +285,19 @@ static void panfrost_mmu_flush_range(struct panfrost_device *pfdev,
>  	pm_runtime_put_autosuspend(pfdev->dev);
>  }
>  
> -static int mmu_map_sg(struct panfrost_device *pfdev, struct panfrost_mmu *mmu,
> +static size_t mmu_map_sg(struct panfrost_device *pfdev, struct panfrost_mmu *mmu,
>  		      u64 iova, int prot, struct sg_table *sgt)
>  {
>  	unsigned int count;
>  	struct scatterlist *sgl;
>  	struct io_pgtable_ops *ops = mmu->pgtbl_ops;
>  	u64 start_iova = iova;
> +	size_t total = 0;
>  
>  	for_each_sgtable_dma_sg(sgt, sgl, count) {
>  		unsigned long paddr = sg_dma_address(sgl);
>  		size_t len = sg_dma_len(sgl);
> +		total += len;
>  
>  		dev_dbg(pfdev->dev, "map: as=%d, iova=%llx, paddr=%lx, len=%zx", mmu->as, iova, paddr, len);
>  
> @@ -315,7 +317,7 @@ static int mmu_map_sg(struct panfrost_device *pfdev, struct panfrost_mmu *mmu,
>  
>  	panfrost_mmu_flush_range(pfdev, mmu, start_iova, iova - start_iova);
>  
> -	return 0;
> +	return total;
>  }
>  
>  int panfrost_mmu_map(struct panfrost_gem_mapping *mapping)
> @@ -447,6 +449,7 @@ static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as,
>  	pgoff_t page_offset;
>  	struct sg_table *sgt;
>  	struct page **pages;
> +	size_t mapped_size;
>  
>  	bomapping = addr_to_mapping(pfdev, as, addr);
>  	if (!bomapping)
> @@ -518,10 +521,11 @@ static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as,
>  	if (ret)
>  		goto err_map;
>  
> -	mmu_map_sg(pfdev, bomapping->mmu, addr,
> -		   IOMMU_WRITE | IOMMU_READ | IOMMU_NOEXEC, sgt);
> +	mapped_size = mmu_map_sg(pfdev, bomapping->mmu, addr,
> +				 IOMMU_WRITE | IOMMU_READ | IOMMU_NOEXEC, sgt);
>  
>  	bomapping->active = true;
> +	bo->heap_rss_size += mapped_size;

The alloc-on-fault granularity is set static (2MB), so no need to
make mmu_map_sg() return the mapped size, we can just do += SZ_2M if
things worked.

>  
>  	dev_dbg(pfdev->dev, "mapped page fault @ AS%d %llx", as, addr);
>