On Mon, Oct 10, 2016 at 11:27:00PM +0100, Chris Wilson wrote:
> commit 1625e7e549c5 ("drm/i915: make compact dma scatter lists creation
> work with SWIOTLB backend") took a heavy handed approach to undo the
> scatterlist compaction in the face of SWIOTLB. (The compaction hit a bug
> whereby we tried to pass a segment larger than SWIOTLB could handle.) We
> can be a little more intelligent and try compacting the scatterlist up
> to the maximum SWIOTLB segment size (when using SWIOTLB).
>
Won't this cause a bigger usage of the SWIOTLB bounce buffer ?
> v2: Tidy sg_mark_end() and cpp
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> CC: Imre Deak <imre.deak@xxxxxxxxx>
> CC: Daniel Vetter <daniel.vetter@xxxxxxxx>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_gem.c | 30 ++++++++++++++++++------------
> 1 file changed, 18 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index dff8d05d80ee..50fd611926cb 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -2201,6 +2201,15 @@ unlock:
> mutex_unlock(&obj->mm.lock);
> }
>
> +static unsigned long swiotlb_max_size(void)
> +{
> +#if IS_ENABLED(CONFIG_SWIOTLB)
> + return swiotlb_nr_tbl() << IO_TLB_SHIFT;
> +#else
> + return 0;
> +#endif
> +}
> +
> static struct sg_table *
> i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
> {
> @@ -2212,6 +2221,7 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
> struct sgt_iter sgt_iter;
> struct page *page;
> unsigned long last_pfn = 0; /* suppress gcc warning */
> + unsigned long max_segment;
> int ret;
> gfp_t gfp;
>
> @@ -2222,6 +2232,10 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
> GEM_BUG_ON(obj->base.read_domains & I915_GEM_GPU_DOMAINS);
> GEM_BUG_ON(obj->base.write_domain & I915_GEM_GPU_DOMAINS);
>
> + max_segment = swiotlb_max_size();
> + if (!max_segment)
> + max_segment = obj->base.size;
> +
> st = kmalloc(sizeof(*st), GFP_KERNEL);
> if (st == NULL)
> return ERR_PTR(-ENOMEM);
> @@ -2263,15 +2277,9 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
> goto err_pages;
> }
> }
> -#ifdef CONFIG_SWIOTLB
> - if (swiotlb_nr_tbl()) {
> - st->nents++;
> - sg_set_page(sg, page, PAGE_SIZE, 0);
> - sg = sg_next(sg);
> - continue;
> - }
> -#endif
> - if (!i || page_to_pfn(page) != last_pfn + 1) {
> + if (!i ||
> + sg->length >= max_segment ||
> + page_to_pfn(page) != last_pfn + 1) {
> if (i)
> sg = sg_next(sg);
> st->nents++;
> @@ -2284,9 +2292,7 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
> /* Check that the i965g/gm workaround works. */
> WARN_ON((gfp & __GFP_DMA32) && (last_pfn >= 0x00100000UL));
> }
> -#ifdef CONFIG_SWIOTLB
> - if (!swiotlb_nr_tbl())
> -#endif
> + if (sg) /* loop terminated early; short sg table */
> sg_mark_end(sg);
>
> ret = i915_gem_gtt_prepare_pages(obj, st);
> --
> 2.9.3
>
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