[Intel-gfx] [PATCH 3/3] drm/i915: mark GEM objects as dirty when written by the CPU

[Chris Wilson]

On Tue, Dec 08, 2015 at 04:51:18PM +0000, Dave Gordon wrote:
> This patch covers a couple more places where a GEM object is (or may be)
> modified by means of CPU writes, and should therefore be marked dirty to
> ensure that the changes are not lost in the evenof of the object is
> evicted under memory pressure.
> 
> It may be possible to optimise these paths later, by marking only
> specific pages of the object as dirty (for objects backed by shmfs
> pages); but for now let's ensure correctness by dirtying the whole
> object.
> 
> Signed-off-by: Dave Gordon <david.s.gordon at intel.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_gem.c        | 4 +++-
>  drivers/gpu/drm/i915/i915_gem_dmabuf.c | 2 ++
>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 12f68f4..36b9539 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -937,7 +937,6 @@ i915_gem_shmem_pwrite(struct drm_device *dev,
>  	i915_gem_object_pin_pages(obj);
>  
>  	offset = args->offset;
> -	obj->dirty = 1;
>  
>  	for_each_sg_page(obj->pages->sgl, &sg_iter, obj->pages->nents,
>  			 offset >> PAGE_SHIFT) {
> @@ -1074,6 +1073,9 @@ i915_gem_pwrite_ioctl(struct drm_device *dev, void *data,
>  		goto out;
>  	}
>  
> +	/* Object backing store will be out of date hereafter */
> +	obj->dirty = 1;

Possibly. I'd rather just have shmem_pwrite be consistent and use
set_page_dirty. It is baked into the code that it doesn't access every
page.

>  	trace_i915_gem_object_pwrite(obj, args->offset, args->size);
>  
>  	ret = -EFAULT;
> diff --git a/drivers/gpu/drm/i915/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/i915_gem_dmabuf.c
> index e9c2bfd..49a74c6 100644
> --- a/drivers/gpu/drm/i915/i915_gem_dmabuf.c
> +++ b/drivers/gpu/drm/i915/i915_gem_dmabuf.c
> @@ -208,6 +208,8 @@ static int i915_gem_begin_cpu_access(struct dma_buf *dma_buf, size_t start, size
>  		return ret;
>  
>  	ret = i915_gem_object_set_to_cpu_domain(obj, write);
> +	if (write)
> +		obj->dirty = 1;

No. The accessor here should already be using set_page_dirty.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre