Re: [Intel-gfx] [PATCH 2/2] drm/i915/gem: Migrate to system at dma-buf attach time (v5)

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Jul 12, 2021 at 06:12:34PM -0500, Jason Ekstrand wrote:
> From: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> 
> Until we support p2p dma or as a complement to that, migrate data
> to system memory at dma-buf attach time if possible.
> 
> v2:
> - Rebase on dynamic exporter. Update the igt_dmabuf_import_same_driver
>   selftest to migrate if we are LMEM capable.
> v3:
> - Migrate also in the pin() callback.
> v4:
> - Migrate in attach
> v5: (jason)
> - Lock around the migration
> 
> Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> Signed-off-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
> Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
> ---
>  drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c    | 25 ++++++++++++++++++-
>  .../drm/i915/gem/selftests/i915_gem_dmabuf.c  |  4 ++-
>  2 files changed, 27 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> index 9a655f69a0671..3163f00554476 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> @@ -170,8 +170,31 @@ static int i915_gem_dmabuf_attach(struct dma_buf *dmabuf,
>  				  struct dma_buf_attachment *attach)
>  {
>  	struct drm_i915_gem_object *obj = dma_buf_to_obj(dmabuf);
> +	struct i915_gem_ww_ctx ww;
> +	int err;
> +
> +	for_i915_gem_ww(&ww, err, true) {
> +		err = i915_gem_object_lock(obj, &ww);
> +		if (err)
> +			continue;
> +
> +		if (!i915_gem_object_can_migrate(obj, INTEL_REGION_SMEM)) {
> +			err = -EOPNOTSUPP;
> +			continue;
> +		}
> +
> +		err = i915_gem_object_migrate(obj, &ww, INTEL_REGION_SMEM);
> +		if (err)
> +			continue;
>  
> -	return i915_gem_object_pin_pages_unlocked(obj);
> +		err = i915_gem_object_wait_migration(obj, 0);
> +		if (err)
> +			continue;
> +
> +		err = i915_gem_object_pin_pages(obj);
> +	}
> +
> +	return err;
>  }
>  
>  static void i915_gem_dmabuf_detach(struct dma_buf *dmabuf,
> diff --git a/drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c
> index 3dc0f8b3cdab0..4f7e77b1c0152 100644
> --- a/drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c
> +++ b/drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c
> @@ -106,7 +106,9 @@ static int igt_dmabuf_import_same_driver(void *arg)
>  	int err;
>  
>  	force_different_devices = true;
> -	obj = i915_gem_object_create_shmem(i915, PAGE_SIZE);
> +	obj = i915_gem_object_create_lmem(i915, PAGE_SIZE, 0);

I'm wondering (and couldn't answer) whether this creates an lmem+smem
buffer, since if we create an lmem-only buffer then the migration above
should fail.

Which I'm also not sure we have a testcase for that testcase either ...

I tried to read some code here, but got a bit lost. Ideas?
-Daniel

> +	if (IS_ERR(obj))
> +		obj = i915_gem_object_create_shmem(i915, PAGE_SIZE);
>  	if (IS_ERR(obj))
>  		goto out_ret;
>  
> -- 
> 2.31.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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