[PATCH v4] drm/xe/migrate: Fix CCS copy for small VRAM copy chunks
Matthew Auld
matthew.william.auld at gmail.com
Mon Dec 18 19:37:30 UTC 2023
On Mon, 18 Dec 2023 at 14:29, Thomas Hellström
<thomas.hellstrom at linux.intel.com> wrote:
>
> Since the migrate code is using the identity map for addressing VRAM,
> copy chunks may become as small as 64K if the VRAM resource is fragmented.
>
> However, a chunk size smaller that 1MiB may lead to the *next* chunk's
> offset into the CCS metadata backup memory may not be page-aligned, and
> the XY_CTRL_SURF_COPY_BLT command can't handle that, and even if it could,
> the current code doesn't handle the offset calculaton correctly.
>
> To fix this, make sure we align the size of VRAM copy chunks to 1MiB. If
> the remaining data to copy is smaller than that, that's not a problem,
> so use the remaining size. If the VRAM copy cunk becomes fragmented due
> to the size alignment restriction, don't use the identity map, but instead
> emit PTEs into the page-table like we do for system memory.
>
> v2:
> - Rebase
> v3:
> - Future proof somewhat by taking into account the real data size to
> flat CCS metadata size ratio. (Matt Roper)
> - Invert a couple of if-statements for better readability.
> - Fix support for 4K-granularity VRAM sizes. (Tested on DG1).
> v4:
> - Fix up code comments
> - Fix debug printout format typo.
>
> Cc: Matt Roper <matthew.d.roper at intel.com>
> Cc: Matthew Auld <matthew.william.auld at gmail.com>
> Cc: Matthew Brost <matthew.brost at intel.com>
> Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> ---
> drivers/gpu/drm/xe/tests/xe_migrate.c | 2 +-
> drivers/gpu/drm/xe/xe_migrate.c | 128 ++++++++++++++++----------
> 2 files changed, 80 insertions(+), 50 deletions(-)
>
> diff --git a/drivers/gpu/drm/xe/tests/xe_migrate.c b/drivers/gpu/drm/xe/tests/xe_migrate.c
> index 7a32faa2f688..a6523df0f1d3 100644
> --- a/drivers/gpu/drm/xe/tests/xe_migrate.c
> +++ b/drivers/gpu/drm/xe/tests/xe_migrate.c
> @@ -331,7 +331,7 @@ static void xe_migrate_sanity_test(struct xe_migrate *m, struct kunit *test)
> xe_res_first_sg(xe_bo_sg(pt), 0, pt->size, &src_it);
>
> emit_pte(m, bb, NUM_KERNEL_PDE - 1, xe_bo_is_vram(pt), false,
> - &src_it, XE_PAGE_SIZE, pt);
> + &src_it, XE_PAGE_SIZE, pt->ttm.resource);
>
> run_sanity_job(m, xe, bb, bb->len, "Writing PTE for our fake PT", test);
>
> diff --git a/drivers/gpu/drm/xe/xe_migrate.c b/drivers/gpu/drm/xe/xe_migrate.c
> index adf1dab5eba2..d8fff0403f74 100644
> --- a/drivers/gpu/drm/xe/xe_migrate.c
> +++ b/drivers/gpu/drm/xe/xe_migrate.c
> @@ -62,6 +62,8 @@ struct xe_migrate {
> * out of the pt_bo.
> */
> struct drm_suballoc_manager vm_update_sa;
> + /** @min_chunk_size: For dgfx, Minimum chunk size */
> + u64 min_chunk_size;
> };
>
> #define MAX_PREEMPTDISABLE_TRANSFER SZ_8M /* Around 1ms. */
> @@ -364,6 +366,19 @@ struct xe_migrate *xe_migrate_init(struct xe_tile *tile)
> if (err)
> return ERR_PTR(err);
>
> + if (IS_DGFX(xe)) {
> + if (xe_device_has_flat_ccs(xe))
> + /* min chunk size corresponds to 4K of CCS Metadata */
> + m->min_chunk_size = SZ_4K * SZ_64K /
> + xe_device_ccs_bytes(xe, SZ_64K);
> + else
> + /* Somewhat arbitrary to avoid a huge amount of blits */
> + m->min_chunk_size = SZ_64K;
> + m->min_chunk_size = roundup_pow_of_two(m->min_chunk_size);
> + drm_dbg(&xe->drm, "Migrate min chunk size is 0x%08llx\n",
> + (unsigned long long)m->min_chunk_size);
> + }
> +
> return m;
> }
>
> @@ -375,16 +390,35 @@ static u64 max_mem_transfer_per_pass(struct xe_device *xe)
> return MAX_PREEMPTDISABLE_TRANSFER;
> }
>
> -static u64 xe_migrate_res_sizes(struct xe_device *xe, struct xe_res_cursor *cur)
> +static u64 xe_migrate_res_sizes(struct xe_migrate *m, struct xe_res_cursor *cur)
> {
> - /*
> - * For VRAM we use identity mapped pages so we are limited to current
> - * cursor size. For system we program the pages ourselves so we have no
> - * such limitation.
> - */
> - return min_t(u64, max_mem_transfer_per_pass(xe),
> - mem_type_is_vram(cur->mem_type) ? cur->size :
> - cur->remaining);
> + struct xe_device *xe = tile_to_xe(m->tile);
> + u64 size = min_t(u64, max_mem_transfer_per_pass(xe), cur->remaining);
> +
> + if (mem_type_is_vram(cur->mem_type)) {
> + /*
> + * VRAM we want to blit in chunks with sizes aligned to
> + * min_chunk_size in order for the offset to CCS metadata to be
> + * page-aligned. If it's the last chunk it may be smaller.
> + *
> + * Another constraint is that we need to limit the blit to
> + * the VRAM block size, unless size is smaller than
> + * min_chunk_size.
> + */
> + u64 chunk = max_t(u64, cur->size, m->min_chunk_size);
> +
> + size = min_t(u64, size, chunk);
> + if (size > m->min_chunk_size)
> + size = round_down(size, m->min_chunk_size);
> + }
> +
> + return size;
Patch makes sense. Just one question here.
Say you have 1G object, but it is ultra fragmented into 64K only
pages. IIUC cur->remaining would be 1G, and cur->size would be 64K.
But with that chunk=1M and the returned size=1M? Shouldn't the
returned size be 64K in this case?
> +}
> +
> +static bool xe_migrate_allow_identity(u64 size, const struct xe_res_cursor *cur)
> +{
> + /* If the chunk is not fragmented, allow identity map. */
> + return cur->size >= size;
> }
>
> static u32 pte_update_size(struct xe_migrate *m,
> @@ -397,7 +431,12 @@ static u32 pte_update_size(struct xe_migrate *m,
> u32 cmds = 0;
>
> *L0_pt = pt_ofs;
> - if (!is_vram) {
> + if (is_vram && xe_migrate_allow_identity(*L0, cur)) {
> + /* Offset into identity map. */
> + *L0_ofs = xe_migrate_vram_ofs(tile_to_xe(m->tile),
> + cur->start + vram_region_gpu_offset(res));
> + cmds += cmd_size;
> + } else {
> /* Clip L0 to available size */
> u64 size = min(*L0, (u64)avail_pts * SZ_2M);
> u64 num_4k_pages = DIV_ROUND_UP(size, XE_PAGE_SIZE);
> @@ -413,11 +452,6 @@ static u32 pte_update_size(struct xe_migrate *m,
>
> /* Each chunk has a single blit command */
> cmds += cmd_size;
> - } else {
> - /* Offset into identity map. */
> - *L0_ofs = xe_migrate_vram_ofs(tile_to_xe(m->tile),
> - cur->start + vram_region_gpu_offset(res));
> - cmds += cmd_size;
> }
>
> return cmds;
> @@ -427,10 +461,10 @@ static void emit_pte(struct xe_migrate *m,
> struct xe_bb *bb, u32 at_pt,
> bool is_vram, bool is_comp_pte,
> struct xe_res_cursor *cur,
> - u32 size, struct xe_bo *bo)
> + u32 size, struct ttm_resource *res)
> {
> struct xe_device *xe = tile_to_xe(m->tile);
> -
> + struct xe_vm *vm = m->q->vm;
> u16 pat_index;
> u32 ptes;
> u64 ofs = at_pt * XE_PAGE_SIZE;
> @@ -443,13 +477,6 @@ static void emit_pte(struct xe_migrate *m,
> else
> pat_index = xe->pat.idx[XE_CACHE_WB];
>
> - /*
> - * FIXME: Emitting VRAM PTEs to L0 PTs is forbidden. Currently
> - * we're only emitting VRAM PTEs during sanity tests, so when
> - * that's moved to a Kunit test, we should condition VRAM PTEs
> - * on running tests.
> - */
> -
> ptes = DIV_ROUND_UP(size, XE_PAGE_SIZE);
>
> while (ptes) {
> @@ -469,20 +496,22 @@ static void emit_pte(struct xe_migrate *m,
>
> addr = xe_res_dma(cur) & PAGE_MASK;
> if (is_vram) {
> - /* Is this a 64K PTE entry? */
> - if ((m->q->vm->flags & XE_VM_FLAG_64K) &&
> - !(cur_ofs & (16 * 8 - 1))) {
> - xe_tile_assert(m->tile, IS_ALIGNED(addr, SZ_64K));
> + if (vm->flags & XE_VM_FLAG_64K) {
> + u64 va = cur_ofs * XE_PAGE_SIZE / 8;
> +
> + xe_assert(xe, (va & (SZ_64K - 1)) ==
> + (addr & (SZ_64K - 1)));
> +
> flags |= XE_PTE_PS64;
> }
>
> - addr += vram_region_gpu_offset(bo->ttm.resource);
> + addr += vram_region_gpu_offset(res);
> devmem = true;
> }
>
> - addr = m->q->vm->pt_ops->pte_encode_addr(m->tile->xe,
> - addr, pat_index,
> - 0, devmem, flags);
> + addr = vm->pt_ops->pte_encode_addr(m->tile->xe,
> + addr, pat_index,
> + 0, devmem, flags);
> bb->cs[bb->len++] = lower_32_bits(addr);
> bb->cs[bb->len++] = upper_32_bits(addr);
>
> @@ -694,8 +723,8 @@ struct dma_fence *xe_migrate_copy(struct xe_migrate *m,
> bool usm = xe->info.has_usm;
> u32 avail_pts = max_mem_transfer_per_pass(xe) / LEVEL0_PAGE_TABLE_ENCODE_SIZE;
>
> - src_L0 = xe_migrate_res_sizes(xe, &src_it);
> - dst_L0 = xe_migrate_res_sizes(xe, &dst_it);
> + src_L0 = xe_migrate_res_sizes(m, &src_it);
> + dst_L0 = xe_migrate_res_sizes(m, &dst_it);
>
> drm_dbg(&xe->drm, "Pass %u, sizes: %llu & %llu\n",
> pass++, src_L0, dst_L0);
> @@ -716,6 +745,7 @@ struct dma_fence *xe_migrate_copy(struct xe_migrate *m,
> &ccs_ofs, &ccs_pt, 0,
> 2 * avail_pts,
> avail_pts);
> + xe_assert(xe, IS_ALIGNED(ccs_it.start, PAGE_SIZE));
> }
>
> /* Add copy commands size here */
> @@ -728,20 +758,20 @@ struct dma_fence *xe_migrate_copy(struct xe_migrate *m,
> goto err_sync;
> }
>
> - if (!src_is_vram)
> - emit_pte(m, bb, src_L0_pt, src_is_vram, true, &src_it, src_L0,
> - src_bo);
> - else
> + if (src_is_vram && xe_migrate_allow_identity(src_L0, &src_it))
> xe_res_next(&src_it, src_L0);
> -
> - if (!dst_is_vram)
> - emit_pte(m, bb, dst_L0_pt, dst_is_vram, true, &dst_it, src_L0,
> - dst_bo);
> else
> + emit_pte(m, bb, src_L0_pt, src_is_vram, true, &src_it, src_L0,
> + src);
> +
> + if (dst_is_vram && xe_migrate_allow_identity(src_L0, &dst_it))
> xe_res_next(&dst_it, src_L0);
> + else
> + emit_pte(m, bb, dst_L0_pt, dst_is_vram, true, &dst_it, src_L0,
> + dst);
>
> if (copy_system_ccs)
> - emit_pte(m, bb, ccs_pt, false, false, &ccs_it, ccs_size, src_bo);
> + emit_pte(m, bb, ccs_pt, false, false, &ccs_it, ccs_size, src);
>
> bb->cs[bb->len++] = MI_BATCH_BUFFER_END;
> update_idx = bb->len;
> @@ -950,7 +980,7 @@ struct dma_fence *xe_migrate_clear(struct xe_migrate *m,
> bool usm = xe->info.has_usm;
> u32 avail_pts = max_mem_transfer_per_pass(xe) / LEVEL0_PAGE_TABLE_ENCODE_SIZE;
>
> - clear_L0 = xe_migrate_res_sizes(xe, &src_it);
> + clear_L0 = xe_migrate_res_sizes(m, &src_it);
>
> drm_dbg(&xe->drm, "Pass %u, size: %llu\n", pass++, clear_L0);
>
> @@ -977,12 +1007,12 @@ struct dma_fence *xe_migrate_clear(struct xe_migrate *m,
>
> size -= clear_L0;
> /* Preemption is enabled again by the ring ops. */
> - if (!clear_vram) {
> - emit_pte(m, bb, clear_L0_pt, clear_vram, true, &src_it, clear_L0,
> - bo);
> - } else {
> + if (clear_vram && xe_migrate_allow_identity(clear_L0, &src_it))
> xe_res_next(&src_it, clear_L0);
> - }
> + else
> + emit_pte(m, bb, clear_L0_pt, clear_vram, true, &src_it, clear_L0,
> + dst);
> +
> bb->cs[bb->len++] = MI_BATCH_BUFFER_END;
> update_idx = bb->len;
>
> --
> 2.42.0
>
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