[Intel-gfx] [PATCH 02/26] drm/i915: Reorder execobject[] to insert non-48b objects into the low 4G

[Joonas Lahtinen]

Quoting Chris Wilson (2018-09-11 14:57:46)
> If the caller supplies more than 4G of objects and than one that has to
> be in the low 4G, it is possible for the low 4G to be full before we
> attempt to find room for the last object that must be there. As we don't
> reorder the two types, every pass hits the same problem and we fail with
> ENOSPC. However, if we impose a little bit of ordering between the two
> classes of objects, on the second pass we will be able to fit the
> special object as we do it first. For setups that only use !48b objects,
> we now reverse the order between passes, hopefully making the subsequent
> passes more likely to succeed given that we are trying a different
> order (rather than repeating the previous pass!)
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>

Might be worthy dropping a one-liner comment in the fashion of.

/* Avoid congesting 4GB region required for last object. */

Reviewed-by: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>

Regards, Joonas

> ---
>  drivers/gpu/drm/i915/i915_gem_execbuffer.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> index 22b4cb775576..d70d142f5338 100644
> --- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> @@ -696,6 +696,8 @@ static int eb_reserve(struct i915_execbuffer *eb)
>                                 list_add(&vma->exec_link, &eb->unbound);
>                         else if (flags & __EXEC_OBJECT_NEEDS_MAP)
>                                 list_add_tail(&vma->exec_link, &eb->unbound);
> +                       else if (!(flags & EXEC_OBJECT_SUPPORTS_48B_ADDRESS))
> +                               list_add(&vma->exec_link, &last);
>                         else
>                                 list_add_tail(&vma->exec_link, &last);
>                 }
> -- 
> 2.19.0.rc2
>