Re: [PATCH 4/4] drm/i915: Use __sg_alloc_table_from_pages for userptr allocations

Chris Wilson
2017-07-28T11:07:10Z

Quoting Tvrtko Ursulin (2017-07-27 10:05:04)
> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>
> With the addition of __sg_alloc_table_from_pages we can control
> the maximum coallescing size and eliminate a separate path for
> allocating backing store here.
>
> Similar to 871dfbd67d4e ("drm/i915: Allow compaction upto
> SWIOTLB max segment size") this enables more compact sg lists to
> be created and so has a beneficial effect on workloads with many
> and/or large objects of this class.
>
> v2:
> * Rename helper to i915_sg_segment_size and fix swiotlb override.
> * Commit message update.
>
> v3:
> * Actually include the swiotlb override fix.
>
> v4:
> * Regroup parameters a bit. (Chris Wilson)
>
> v5:
> * Rebase for swiotlb_max_segment.
> * Add DMA map failure handling as in abb0deacb5a6
> ("drm/i915: Fallback to single PAGE_SIZE segments for DMA remapping").
>
> v6: Handle swiotlb_max_segment() returning 1. (Joonas Lahtinen)
>
> v7: Rebase.
>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: linux-kernel@vger.kernel.org
> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> (v4)
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> ---
> drivers/gpu/drm/i915/i915_drv.h | 15 +++++++
> drivers/gpu/drm/i915/i915_gem.c | 6 +--
> drivers/gpu/drm/i915/i915_gem_userptr.c | 79 ++++++++++++---------------------
> 3 files changed, 45 insertions(+), 55 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 2c7456f4ed38..6383940e8d55 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2749,6 +2749,21 @@ static inline struct scatterlist *__sg_next(struct scatterlist *sg)
> (((__iter).curr += PAGE_SIZE) < (__iter).max) || \
> ((__iter) = __sgt_iter(__sg_next((__iter).sgp), false), 0))
>
> +static inline unsigned int i915_sg_segment_size(void)
> +{
> + unsigned int size = swiotlb_max_segment();
> +
> + if (size == 0)
> + return SCATTERLIST_MAX_SEGMENT;
> +
> + size = rounddown(size, PAGE_SIZE);

Looks like swiotbl_max_seqment() is always page aligned when not 1.
And it returns bytes, ok.

Given that you are using a pot, you can use round_down().

> + /* swiotlb_max_segment_size can return 1 byte when it means one page. */
> + if (size < PAGE_SIZE)
> + size = PAGE_SIZE;
> +
> + return size;
> +}
> +
> static inline const struct intel_device_info *
> intel_info(const struct drm_i915_private *dev_priv)
> {
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 6faabf34f142..a60885d6231b 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -2339,7 +2339,7 @@ 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 int max_segment;
> + unsigned int max_segment = i915_sg_segment_size();
> gfp_t noreclaim;
> int ret;
>
> @@ -2350,10 +2350,6 @@ 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_segment();
> - if (!max_segment)
> - max_segment = rounddown(UINT_MAX, PAGE_SIZE);

Conversion to i915_sg_segment_size(), ok.

> -
> st = kmalloc(sizeof(*st), GFP_KERNEL);
> if (st == NULL)
> return ERR_PTR(-ENOMEM);
> diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
> index ccd09e8419f5..60c10d4118ae 100644
> --- a/drivers/gpu/drm/i915/i915_gem_userptr.c
> +++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
> @@ -399,64 +399,42 @@ struct get_pages_work {
> struct task_struct *task;
> };
>
> -#if IS_ENABLED(CONFIG_SWIOTLB)
> -#define swiotlb_active() swiotlb_nr_tbl()
> -#else
> -#define swiotlb_active() 0
> -#endif

Converted to i915_sg_segment_size(), nice.

> -static int
> -st_set_pages(struct sg_table **st, struct page **pvec, int num_pages)
> -{
> - struct scatterlist *sg;
> - int ret, n;
> -
> - *st = kmalloc(sizeof(**st), GFP_KERNEL);
> - if (*st == NULL)
> - return -ENOMEM;
> -
> - if (swiotlb_active()) {
> - ret = sg_alloc_table(*st, num_pages, GFP_KERNEL);
> - if (ret)
> - goto err;
> -
> - for_each_sg((*st)->sgl, sg, num_pages, n)
> - sg_set_page(sg, pvec[n], PAGE_SIZE, 0);
> - } else {
> - ret = sg_alloc_table_from_pages(*st, pvec, num_pages,
> - 0, num_pages << PAGE_SHIFT,
> - GFP_KERNEL);
> - if (ret)
> - goto err;
> - }
> -
> - return 0;
> -
> -err:
> - kfree(*st);
> - *st = NULL;
> - return ret;
> -}
> -
> static struct sg_table *
> -__i915_gem_userptr_set_pages(struct drm_i915_gem_object *obj,
> - struct page **pvec, int num_pages)
> +__i915_gem_userptr_alloc_pages(struct drm_i915_gem_object *obj,
> + struct page **pvec, int num_pages)
> {
> - struct sg_table *pages;
> + unsigned int max_segment = i915_sg_segment_size();
> + struct sg_table *st;
> int ret;
>
> - ret = st_set_pages(&pages, pvec, num_pages);
> - if (ret)
> + st = kmalloc(sizeof(*st), GFP_KERNEL);
> + if (!st)
> + return ERR_PTR(-ENOMEM);
> +
> +alloc_table:
> + ret = __sg_alloc_table_from_pages(st, pvec, num_pages,
> + 0, num_pages << PAGE_SHIFT,
> + max_segment,
> + GFP_KERNEL);
> + if (ret) {
> + kfree(st);
> return ERR_PTR(ret);
> + }
>
> - ret = i915_gem_gtt_prepare_pages(obj, pages);
> + ret = i915_gem_gtt_prepare_pages(obj, st);
> if (ret) {
> - sg_free_table(pages);
> - kfree(pages);
> + sg_free_table(st);
> +
> + if (max_segment > PAGE_SIZE) {
> + max_segment = PAGE_SIZE;
> + goto alloc_table;
> + }
> +
> + kfree(st);
> return ERR_PTR(ret);
> }

Much neater.

>
> - return pages;
> + return st;
> }
>
> static int
> @@ -540,7 +518,8 @@ __i915_gem_userptr_get_pages_worker(struct work_struct *_work)
> struct sg_table *pages = ERR_PTR(ret);
>
> if (pinned == npages) {
> - pages = __i915_gem_userptr_set_pages(obj, pvec, npages);
> + pages = __i915_gem_userptr_alloc_pages(obj, pvec,
> + npages);
> if (!IS_ERR(pages)) {
> __i915_gem_object_set_pages(obj, pages);
> pinned = 0;
> @@ -661,7 +640,7 @@ i915_gem_userptr_get_pages(struct drm_i915_gem_object *obj)
> pages = __i915_gem_userptr_get_pages_schedule(obj);
> active = pages == ERR_PTR(-EAGAIN);
> } else {
> - pages = __i915_gem_userptr_set_pages(obj, pvec, num_pages);
> + pages = __i915_gem_userptr_alloc_pages(obj, pvec, num_pages);
> active = !IS_ERR(pages);
> }
> if (active)

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
-Chris