Quoting Matthew Auld (2020-11-27 12:06:53)
> +int i915_window_blt_copy(struct drm_i915_gem_object *dst,
> + struct drm_i915_gem_object *src)
> +{
> + struct drm_i915_private *i915 = to_i915(src->base.dev);
> + struct intel_context *ce = i915->gt.engine[BCS0]->blitter_context;
> + bool src_is_lmem = i915_gem_object_is_lmem(src);
> + bool dst_is_lmem = i915_gem_object_is_lmem(dst);
> + struct scatterlist *last_sgl;
> + struct i915_vma *src_vma, *dst_vma;
> + struct i915_request *rq;
> + u64 cur_win_sz, blt_copied, offset;
> + long timeout;
> + u32 size;
> + int err;
> +
> + src_vma = src_is_lmem ? i915->mm.lmem_window[0] :
> + i915->mm.smem_window[0];
> + dst_vma = dst_is_lmem ? i915->mm.lmem_window[1] :
> + i915->mm.smem_window[1];
> +
> + if (!src_vma || !dst_vma)
> + return -ENODEV;
> +
> + blt_copied = 0;
> +
> + err = i915_window_blt_copy_prepare_obj(src);
> + if (err)
> + return err;
> +
> + err = i915_window_blt_copy_prepare_obj(dst);
> + if (err) {
> + i915_gem_object_unpin_pages(src);
> + return err;
> + }
> +
> + mutex_lock(&i915->mm.window_mutex);
> + src_vma->obj = src;
> + dst_vma->obj = dst;
> + do {
> + cur_win_sz = min_t(u64, BLT_WINDOW_SZ,
> + (src->base.size - blt_copied));
> + offset = blt_copied >> PAGE_SHIFT;
> + size = ALIGN(cur_win_sz, src->mm.region->min_page_size) >>
> + PAGE_SHIFT;
> + intel_partial_pages_for_sg_table(src, src_vma->pages, offset,
> + size, &last_sgl);
> +
> + /*
> + * Insert pages into vm, expects the pages to the full
> + * length of VMA. But we may have the pages of <= vma_size.
> + * Hence altering the vma size to match the total size of
> + * the pages attached.
> + */
> + src_vma->size = size << PAGE_SHIFT;
> + i915_insert_vma_pages(src_vma, src_is_lmem);
> + sg_unmark_end(last_sgl);
> +
> + /*
> + * Source obj size could be smaller than the dst obj size,
> + * due to the varying min_page_size of the mem regions the
> + * obj belongs to. But when we insert the pages into vm,
> + * the total size of the pages supposed to be multiples of
> + * the min page size of that mem region.
> + */
> + size = ALIGN(cur_win_sz, dst->mm.region->min_page_size) >>
> + PAGE_SHIFT;
> + intel_partial_pages_for_sg_table(dst, dst_vma->pages, offset,
> + size, &last_sgl);
> +
> + dst_vma->size = size << PAGE_SHIFT;
> + i915_insert_vma_pages(dst_vma, dst_is_lmem);
> + sg_unmark_end(last_sgl);
> +
> + rq = i915_request_create(ce);
> + if (IS_ERR(rq)) {
> + err = PTR_ERR(rq);
> + break;
> + }
> + if (rq->engine->emit_init_breadcrumb) {
> + err = rq->engine->emit_init_breadcrumb(rq);
> + if (unlikely(err)) {
> + DRM_ERROR("init_breadcrumb failed. %d\n", err);
> + break;
> + }
> + }
> + err = i915_window_blt_copy_batch_prepare(rq, src_vma, dst_vma,
> + cur_win_sz);
> + if (err) {
> + DRM_ERROR("Batch preparation failed. %d\n", err);
> + i915_request_set_error_once(rq, -EIO);
> + }
> +
> + i915_request_get(rq);
> + i915_request_add(rq);
> +
> + timeout = i915_request_wait(rq, 0, MAX_SCHEDULE_TIMEOUT);
Locked waits.
> + if (timeout < 0) {
> + DRM_ERROR("BLT Request is not completed. %ld\n",
> + timeout);
> + err = timeout;
> + i915_request_put(rq);
> + break;
> + }
> +
> + blt_copied += cur_win_sz;
> + err = 0;
> + i915_request_put(rq);
> + flush_work(&i915->gt.engine[BCS0]->retire_work);
Papering (doubtful the paper is successful) over bugs by introducing a
whole load more.
This fails the basic premise that eviction must be pipelined. The PTE
are transient and can be written prior to the copy and kept within the
non-preemptible window of the blt. Thus allowing many evictions to
scheduled in parallel (by either allocating separate contexts, or more
preferably picking a user context).
-Chris
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