[PATCH v2] drm/xe: Do not blindly copy system CCS pages when shrinking

[Matthew Brost <matthew.brost@intel.com>]

If the PAT index for a BO is configured without compression, copying CCS
pages during BO shrinking provides no value. Skip CCS copies for BOs that
have never been configured with compressed PAT indexes.

Once a BO is configured with a compressed PAT index, this becomes a
one-way transition that enables CCS copies. This heuristic is imprecise,
but simple and functional.

Assisted-by: Claude:claude-sonnet-4.6 # kernel doc
Signed-off-by: Matthew Brost <matthew.brost@intel.com>

---

When running 10x tabs webgl aquarium, it was observed a ratio of ~6.5 to
1 of BOs that can possible enable compression (xe_bo_needs_ccs_pages
returns true) actually enable compression in the PAT index and overall
CCS copies are reduced by roughly 1/2 when the shrinker is triggered.

v2:
 - Only skip CCS copy when moving to system placement (sashiko)
 - Set ccs_used upon rebind (sashiko)
 - Add helpers for ccs_used access + document locking
 - Set ccs_used in kunit tests (CI)
---
 drivers/gpu/drm/xe/tests/xe_bo.c |  2 ++
 drivers/gpu/drm/xe/xe_bo.c       |  3 +++
 drivers/gpu/drm/xe/xe_bo.h       | 35 ++++++++++++++++++++++++++++++++
 drivers/gpu/drm/xe/xe_bo_types.h |  6 ++++++
 drivers/gpu/drm/xe/xe_vm.c       |  8 ++++++++
 5 files changed, 54 insertions(+)

diff --git a/drivers/gpu/drm/xe/tests/xe_bo.c b/drivers/gpu/drm/xe/tests/xe_bo.c
index 49c95ed67d7e..1686e735a2c7 100644
--- a/drivers/gpu/drm/xe/tests/xe_bo.c
+++ b/drivers/gpu/drm/xe/tests/xe_bo.c
@@ -149,6 +149,8 @@ static void ccs_test_run_tile(struct xe_device *xe, struct xe_tile *tile,
 
 	xe_bo_lock(bo, false);
 
+	xe_bo_set_ccs_used(bo);
+
 	kunit_info(test, "Verifying that CCS data is cleared on creation.\n");
 	ret = ccs_test_migrate(tile, bo, false, 0ULL, 0xdeadbeefdeadbeefULL,
 			       test, exec);
diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
index 5ce60d161e09..765b5d345a7e 100644
--- a/drivers/gpu/drm/xe/xe_bo.c
+++ b/drivers/gpu/drm/xe/xe_bo.c
@@ -1105,6 +1105,9 @@ static int xe_bo_move(struct ttm_buffer_object *ttm_bo, bool evict,
 			flags |= XE_MIGRATE_CLEAR_FLAG_CCS_DATA;
 
 		fence = xe_migrate_clear(migrate, bo, new_mem, flags);
+	} else if (handle_system_ccs && new_mem->mem_type == XE_PL_SYSTEM &&
+		   !xe_bo_is_ccs_used(bo)) {
+		fence = dma_fence_get_stub();
 	} else {
 		fence = xe_migrate_copy(migrate, bo, bo, old_mem, new_mem,
 					handle_system_ccs);
diff --git a/drivers/gpu/drm/xe/xe_bo.h b/drivers/gpu/drm/xe/xe_bo.h
index 68dea7d25a6b..101dc7a36f9a 100644
--- a/drivers/gpu/drm/xe/xe_bo.h
+++ b/drivers/gpu/drm/xe/xe_bo.h
@@ -514,4 +514,39 @@ static inline bool xe_bo_is_mem_type(struct xe_bo *bo, u32 mem_type)
 	xe_bo_assert_held(bo);
 	return bo->ttm.resource->mem_type == mem_type;
 }
+
+/**
+ * xe_bo_set_ccs_used() - Mark the CCS region of a BO as used
+ * @bo: The &xe_bo whose CCS region is being marked as used
+ *
+ * Mark the CCS (Compression Control Surface) metadata region of @bo as in use.
+ * This is set when the BO is mapped with a PAT index that has compression
+ * enabled, indicating that the CCS region holds valid compression state and
+ * must be handled appropriately during migration (e.g. copied or cleared rather
+ * than skipped).
+ *
+ * Caller must hold the BO reservation lock.
+ */
+static inline void xe_bo_set_ccs_used(struct xe_bo *bo)
+{
+	xe_bo_assert_held(bo);
+	bo->ccs_used = true;
+}
+
+/**
+ * xe_bo_is_ccs_used() - Check whether the CCS region of a BO is in use
+ * @bo: The &xe_bo to check
+ *
+ * Return: true if the CCS (Compression Control Surface) metadata region of
+ * @bo has been marked as used (i.e. the BO was mapped with compression
+ * enabled), false otherwise.
+ *
+ * Caller must hold the BO reservation lock.
+ */
+static inline bool xe_bo_is_ccs_used(struct xe_bo *bo)
+{
+	xe_bo_assert_held(bo);
+	return bo->ccs_used;
+}
+
 #endif
diff --git a/drivers/gpu/drm/xe/xe_bo_types.h b/drivers/gpu/drm/xe/xe_bo_types.h
index 9c199badd9b2..16cb97a5f2a6 100644
--- a/drivers/gpu/drm/xe/xe_bo_types.h
+++ b/drivers/gpu/drm/xe/xe_bo_types.h
@@ -88,6 +88,12 @@ struct xe_bo {
 	/** @ccs_cleared: true means that CCS region of BO is already cleared */
 	bool ccs_cleared;
 
+	/**
+	 * @ccs_used: true means that CCS region of BO is used, protected by
+	 * BO's dma-resv lock
+	 */
+	bool ccs_used;
+
 	/** @bb_ccs: BB instructions of CCS read/write. Valid only for VF */
 	struct xe_mem_pool_node *bb_ccs[XE_SRIOV_VF_CCS_CTX_COUNT];
 
diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
index c3836f6eab35..7fbf3607b48b 100644
--- a/drivers/gpu/drm/xe/xe_vm.c
+++ b/drivers/gpu/drm/xe/xe_vm.c
@@ -743,11 +743,16 @@ static int xe_vm_ops_add_rebind(struct xe_vma_ops *vops, struct xe_vma *vma,
 				u8 tile_mask)
 {
 	struct xe_vma_op *op;
+	struct xe_bo *bo = xe_vma_bo(vma);
 
 	op = kzalloc_obj(*op);
 	if (!op)
 		return -ENOMEM;
 
+	if (bo && xe_pat_index_get_comp_en(xe_vma_vm(vma)->xe,
+					   vma->attr.pat_index))
+		xe_bo_set_ccs_used(bo);
+
 	xe_vm_populate_rebind(op, vma, tile_mask);
 	list_add_tail(&op->link, &vops->list);
 	xe_vma_ops_incr_pt_update_ops(vops, tile_mask, 1);
@@ -3054,6 +3059,9 @@ static int vma_lock_and_validate(struct drm_exec *exec, struct xe_vma *vma,
 
 		if (flags.request_decompress)
 			err = xe_bo_decompress(bo);
+
+		if (xe_pat_index_get_comp_en(vm->xe, vma->attr.pat_index))
+			xe_bo_set_ccs_used(bo);
 	}
 
 	return err;
-- 
2.34.1