Quoting Tvrtko Ursulin (2018-09-26 09:03:53)
> From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
>
> Partial views are small but there can be many of them, and since the sg
> list space for them is allocated pessimistically, we can save some slab by
> trimming the unused tail entries.
>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
> ---
> On the other hand with the diminishing importance of mmap ggtt do we
> expect to see partial views in use these days?
We have over a decade of hw that depends on them, and mesa is still not
entirely rid of them (and there's always i915_dri.so). So partials are
very much sticking around for a long time to come.
> ---
> drivers/gpu/drm/i915/i915_drv.h | 2 ++
> drivers/gpu/drm/i915/i915_gem.c | 2 +-
> drivers/gpu/drm/i915/i915_gem_gtt.c | 2 ++
> 3 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 8624b4bdc242..0fe22263aa9b 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2323,6 +2323,8 @@ static inline struct scatterlist *__sg_next(struct scatterlist *sg)
> (((__iter).curr += PAGE_SIZE) >= (__iter).max) ? \
> (__iter) = __sgt_iter(__sg_next((__iter).sgp), false), 0 : 0)
>
> +bool i915_sg_trim(struct sg_table *orig_st);
> +
> static inline unsigned int i915_sg_page_sizes(struct scatterlist *sg)
> {
> unsigned int page_sizes;
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index db9688d14912..7156ddef178b 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -2491,7 +2491,7 @@ void __i915_gem_object_put_pages(struct drm_i915_gem_object *obj,
> mutex_unlock(&obj->mm.lock);
> }
>
> -static bool i915_sg_trim(struct sg_table *orig_st)
> +bool i915_sg_trim(struct sg_table *orig_st)
> {
> struct sg_table new_st;
> struct scatterlist *sg, *new_sg;
You can spare me having to move a few lines later if you move this to
i915_scatterlist_utils.c?
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> index f6c7ab413081..1ec721c20581 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> @@ -3835,6 +3835,8 @@ intel_partial_pages(const struct i915_ggtt_view *view,
> count -= len >> PAGE_SHIFT;
> if (count == 0) {
> sg_mark_end(sg);
> + i915_sg_trim(st); /* Drop any unused tail entries. */
> +
Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
-Chris
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