Re: [PATCH v2 21/26] drm/xe/migrate: Add function to copy of VRAM data in chunks

[Michal Wajdeczko <michal.wajdeczko@intel.com>]

On 10/22/2025 12:41 AM, Michał Winiarski wrote:
> From: Lukasz Laguna <lukasz.laguna@intel.com>
> 
> Introduce a new function to copy data between VRAM and sysmem objects.
> The existing xe_migrate_copy() is tailored for eviction and restore
> operations, which involves additional logic and operates on entire
> objects.
> The xe_migrate_vram_copy_chunk() allows copying chunks of data to or
> from a dedicated buffer object, which is essential in case of VF
> migration.
> 
> Signed-off-by: Lukasz Laguna <lukasz.laguna@intel.com>
> Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_migrate.c | 134 ++++++++++++++++++++++++++++++--
>  drivers/gpu/drm/xe/xe_migrate.h |   8 ++
>  2 files changed, 136 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_migrate.c b/drivers/gpu/drm/xe/xe_migrate.c
> index 3112c966c67d7..d30675707162b 100644
> --- a/drivers/gpu/drm/xe/xe_migrate.c
> +++ b/drivers/gpu/drm/xe/xe_migrate.c
> @@ -514,7 +514,7 @@ int xe_migrate_init(struct xe_migrate *m)
>  
>  static u64 max_mem_transfer_per_pass(struct xe_device *xe)
>  {
> -	if (!IS_DGFX(xe) && xe_device_has_flat_ccs(xe))
> +	if ((!IS_DGFX(xe) || IS_SRIOV_PF(xe)) && xe_device_has_flat_ccs(xe))

being a PF is permanent case, while your expected usage is only during of the handling of the VF migration.

maybe it would be better to introduce flag FORCE_CCS_LIMITED_TRANSFER and pass it to the migration calls when really needed ?


>  		return MAX_CCS_LIMITED_TRANSFER;
>  
>  	return MAX_PREEMPTDISABLE_TRANSFER;
> @@ -1155,6 +1155,133 @@ struct xe_exec_queue *xe_migrate_exec_queue(struct xe_migrate *migrate)
>  	return migrate->q;
>  }
>  
> +/**
> + * xe_migrate_vram_copy_chunk() - Copy a chunk of a VRAM buffer object.
> + * @vram_bo: The VRAM buffer object.
> + * @vram_offset: The VRAM offset.
> + * @sysmem_bo: The sysmem buffer object.
> + * @sysmem_offset: The sysmem offset.
> + * @size: The size of VRAM chunk to copy.
> + * @dir: The direction of the copy operation.
> + *
> + * Copies a portion of a buffer object between VRAM and system memory.
> + * On Xe2 platforms that support flat CCS, VRAM data is decompressed when
> + * copying to system memory.
> + *
> + * Return: Pointer to a dma_fence representing the last copy batch, or
> + * an error pointer on failure. If there is a failure, any copy operation
> + * started by the function call has been synced.
> + */
> +struct dma_fence *xe_migrate_vram_copy_chunk(struct xe_bo *vram_bo, u64 vram_offset,
> +					     struct xe_bo *sysmem_bo, u64 sysmem_offset,
> +					     u64 size, enum xe_migrate_copy_dir dir)
> +{
> +	struct xe_device *xe = xe_bo_device(vram_bo);
> +	struct xe_tile *tile = vram_bo->tile;
> +	struct xe_gt *gt = tile->primary_gt;
> +	struct xe_migrate *m = tile->migrate;
> +	struct dma_fence *fence = NULL;
> +	struct ttm_resource *vram = vram_bo->ttm.resource;
> +	struct ttm_resource *sysmem = sysmem_bo->ttm.resource;
> +	struct xe_res_cursor vram_it, sysmem_it;
> +	u64 vram_L0_ofs, sysmem_L0_ofs;
> +	u32 vram_L0_pt, sysmem_L0_pt;
> +	u64 vram_L0, sysmem_L0;
> +	bool to_sysmem = (dir == XE_MIGRATE_COPY_TO_SRAM);
> +	bool use_comp_pat = to_sysmem &&
> +		GRAPHICS_VER(xe) >= 20 && xe_device_has_flat_ccs(xe);
> +	int pass = 0;
> +	int err;
> +
> +	xe_assert(xe, IS_ALIGNED(vram_offset | sysmem_offset | size, PAGE_SIZE));
> +	xe_assert(xe, xe_bo_is_vram(vram_bo));
> +	xe_assert(xe, !xe_bo_is_vram(sysmem_bo));
> +	xe_assert(xe, !range_overflows(vram_offset, size, (u64)vram_bo->ttm.base.size));
> +	xe_assert(xe, !range_overflows(sysmem_offset, size, (u64)sysmem_bo->ttm.base.size));
> +
> +	xe_res_first(vram, vram_offset, size, &vram_it);
> +	xe_res_first_sg(xe_bo_sg(sysmem_bo), sysmem_offset, size, &sysmem_it);
> +
> +	while (size) {
> +		u32 pte_flags = PTE_UPDATE_FLAG_IS_VRAM;
> +		u32 batch_size = 2; /* arb_clear() + MI_BATCH_BUFFER_END */
> +		struct xe_sched_job *job;
> +		struct xe_bb *bb;
> +		u32 update_idx;
> +		bool usm = xe->info.has_usm;
> +		u32 avail_pts = max_mem_transfer_per_pass(xe) / LEVEL0_PAGE_TABLE_ENCODE_SIZE;
> +
> +		sysmem_L0 = xe_migrate_res_sizes(m, &sysmem_it);
> +		vram_L0 = min(xe_migrate_res_sizes(m, &vram_it), sysmem_L0);
> +
> +		drm_dbg(&xe->drm, "Pass %u, size: %llu\n", pass++, vram_L0);

nit: there is xe_dbg()

> +
> +		pte_flags |= use_comp_pat ? PTE_UPDATE_FLAG_IS_COMP_PTE : 0;
> +		batch_size += pte_update_size(m, pte_flags, vram, &vram_it, &vram_L0,
> +					      &vram_L0_ofs, &vram_L0_pt, 0, 0, avail_pts);
> +
> +		batch_size += pte_update_size(m, 0, sysmem, &sysmem_it, &vram_L0, &sysmem_L0_ofs,
> +					      &sysmem_L0_pt, 0, avail_pts, avail_pts);
> +		batch_size += EMIT_COPY_DW;
> +
> +		bb = xe_bb_new(gt, batch_size, usm);
> +		if (IS_ERR(bb)) {
> +			err = PTR_ERR(bb);
> +			return ERR_PTR(err);
> +		}
> +
> +		if (xe_migrate_allow_identity(vram_L0, &vram_it))
> +			xe_res_next(&vram_it, vram_L0);
> +		else
> +			emit_pte(m, bb, vram_L0_pt, true, use_comp_pat, &vram_it, vram_L0, vram);
> +
> +		emit_pte(m, bb, sysmem_L0_pt, false, false, &sysmem_it, vram_L0, sysmem);
> +
> +		bb->cs[bb->len++] = MI_BATCH_BUFFER_END;
> +		update_idx = bb->len;
> +
> +		if (to_sysmem)
> +			emit_copy(gt, bb, vram_L0_ofs, sysmem_L0_ofs, vram_L0, XE_PAGE_SIZE);
> +		else
> +			emit_copy(gt, bb, sysmem_L0_ofs, vram_L0_ofs, vram_L0, XE_PAGE_SIZE);
> +
> +		job = xe_bb_create_migration_job(m->q, bb, xe_migrate_batch_base(m, usm),
> +						 update_idx);
> +		if (IS_ERR(job)) {
> +			err = PTR_ERR(job);
> +			goto err;

this goto inside 'while' loop is weird

> +		}
> +
> +		xe_sched_job_add_migrate_flush(job, MI_INVALIDATE_TLB);
> +
> +		WARN_ON_ONCE(!dma_resv_test_signaled(vram_bo->ttm.base.resv,
> +						     DMA_RESV_USAGE_BOOKKEEP));
> +		WARN_ON_ONCE(!dma_resv_test_signaled(sysmem_bo->ttm.base.resv,
> +						     DMA_RESV_USAGE_BOOKKEEP));

xe_WARN_ON_ONCE() ?

but why do not use asserts() if we are sure that this shouldn't happen ?

> +
> +		mutex_lock(&m->job_mutex);

scoped_quard(mutex) ?

> +		xe_sched_job_arm(job);
> +		dma_fence_put(fence);
> +		fence = dma_fence_get(&job->drm.s_fence->finished);
> +		xe_sched_job_push(job);
> +
> +		dma_fence_put(m->fence);
> +		m->fence = dma_fence_get(fence);

> +		mutex_unlock(&m->job_mutex);
> +
> +		xe_bb_free(bb, fence);
> +		size -= vram_L0;
> +		continue;
> +
> +err:
> +		xe_bb_free(bb, NULL);
> +
> +		return ERR_PTR(err);
> +	}
> +
> +	return fence;
> +}
> +
>  static void emit_clear_link_copy(struct xe_gt *gt, struct xe_bb *bb, u64 src_ofs,
>  				 u32 size, u32 pitch)
>  {
> @@ -1852,11 +1979,6 @@ static bool xe_migrate_vram_use_pde(struct drm_pagemap_addr *sram_addr,
>  	return true;
>  }
>  
> -enum xe_migrate_copy_dir {
> -	XE_MIGRATE_COPY_TO_VRAM,
> -	XE_MIGRATE_COPY_TO_SRAM,
> -};
> -
>  #define XE_CACHELINE_BYTES	64ull
>  #define XE_CACHELINE_MASK	(XE_CACHELINE_BYTES - 1)
>  
> diff --git a/drivers/gpu/drm/xe/xe_migrate.h b/drivers/gpu/drm/xe/xe_migrate.h
> index 4fad324b62535..d7bcc6ad8464e 100644
> --- a/drivers/gpu/drm/xe/xe_migrate.h
> +++ b/drivers/gpu/drm/xe/xe_migrate.h
> @@ -28,6 +28,11 @@ struct xe_vma;
>  
>  enum xe_sriov_vf_ccs_rw_ctxs;
>  
> +enum xe_migrate_copy_dir {
> +	XE_MIGRATE_COPY_TO_VRAM,
> +	XE_MIGRATE_COPY_TO_SRAM,
> +};

nit: it's time for xe_migrate_types.h ;)

but not as part of this series

> +
>  /**
>   * struct xe_migrate_pt_update_ops - Callbacks for the
>   * xe_migrate_update_pgtables() function.
> @@ -131,6 +136,9 @@ int xe_migrate_ccs_rw_copy(struct xe_tile *tile, struct xe_exec_queue *q,
>  
>  struct xe_lrc *xe_migrate_lrc(struct xe_migrate *migrate);
>  struct xe_exec_queue *xe_migrate_exec_queue(struct xe_migrate *migrate);
> +struct dma_fence *xe_migrate_vram_copy_chunk(struct xe_bo *vram_bo, u64 vram_offset,
> +					     struct xe_bo *sysmem_bo, u64 sysmem_offset,
> +					     u64 size, enum xe_migrate_copy_dir dir);
>  int xe_migrate_access_memory(struct xe_migrate *m, struct xe_bo *bo,
>  			     unsigned long offset, void *buf, int len,
>  			     int write);