On 19/12/2016 12:43, Chris Wilson wrote:
If we at first do not succeed with attempting to remap our physical pages using a coalesced scattergather list, try again with one scattergather entry per page. This should help with swiotlb as it uses a limited buffer size and only searches for contiguous chunks within its buffer aligned up to the next boundary - i.e. we may prematurely cause a failure as we are unable to utilize the unused space between large chunks and trigger an error such as:i915 0000:00:02.0: swiotlb buffer is full (sz: 1630208 bytes) Reported-by: Juergen Gross <jgr...@suse.com> Fixes: 871dfbd67d4e ("drm/i915: Allow compaction upto SWIOTLB max segment size") Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursu...@intel.com> Cc: Imre Deak <imre.d...@intel.com> Cc: <drm-intel-fi...@lists.freedesktop.org> --- drivers/gpu/drm/i915/i915_gem.c | 26 ++++++++++++++++++++++---- 1 file changed, 22 insertions(+), 4 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index 412f3513f269..4e263df2afc3 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -2326,7 +2326,8 @@ static struct sg_table * i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj) { struct drm_i915_private *dev_priv = to_i915(obj->base.dev); - int page_count, i; + const unsigned long page_count = obj->base.size / PAGE_SIZE; + unsigned long i; struct address_space *mapping; struct sg_table *st; struct scatterlist *sg; @@ -2352,7 +2353,7 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj) if (st == NULL) return ERR_PTR(-ENOMEM); - page_count = obj->base.size / PAGE_SIZE; +rebuild_st: if (sg_alloc_table(st, page_count, GFP_KERNEL)) { kfree(st); return ERR_PTR(-ENOMEM); @@ -2411,8 +2412,25 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj) i915_sg_trim(st); ret = i915_gem_gtt_prepare_pages(obj, st); - if (ret) - goto err_pages; + if (ret) { + /* DMA remapping failed? One possible cause is that + * it could not reserve enough large entries, asking + * for PAGE_SIZE chunks instead may be helpful. + */ + if (max_segment > PAGE_SIZE) { + for_each_sgt_page(page, sgt_iter, st) + put_page(page); + sg_free_table(st); + + max_segment = PAGE_SIZE; + goto rebuild_st; + } else { + dev_warn(&dev_priv->drm.pdev->dev, + "Failed to DMA remap %lu pages\n", + page_count); + goto err_pages; + } + } if (i915_gem_object_needs_bit17_swizzle(obj)) i915_gem_object_do_bit_17_swizzle(obj, st);
How much is the cost of freeing and re-acquiring pages in the fall back case? It could be avoidable by using the table and adding something like sgt = i915_sg_copy(sgt, table_max_segment). But it depends on how likely is this path to be hit on swiotlb platforms. I have no idea. Our datasets are much bigger than the swiotlb space - if that is true on such platforms?
Regards, Tvrtko _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx
