[PATCH 2/2] Revert "drm/xe/lnl: Offload system clear page activity to GPU"

[Nirmoy Das <nirmoy.das@intel.com>]

This optimization relied on having to clear CCS on allocations.
If there is no need to clear CCS on allocations then this would mostly
help in reducing CPU utilization.

Revert this patch because of:
1 Currently Xe can't do clear on free and using a invalid ttm flag,
TTM_TT_FLAG_CLEARED_ON_FREE which could poison global ttm pool on
multi-device setup.

2 BO with WB caching type can't have compression enabled so there
is no need to do clear CCS for such allocation. Reducing CPU
utilization is a plus but latency is more important.

Without this patch:
UsmMemoryAllocation(api=l0 type=Host size=4KB)  113.1 us
UsmMemoryAllocation(api=l0 type=Host size=1GB)  91452.6 us
13.93% api_overhead_be  [kernel.kallsyms] [k] pages_are_mergeable
7.59%  api_overhead_be  [kernel.kallsyms] [k] __lock_acquire
3.86%  api_overhead_be  [kernel.kallsyms] [k] lock_is_held_type
3.39%  api_overhead_be  [kernel.kallsyms] [k] rcu_is_watching
3.37%  api_overhead_be  [xe]              [k] emit_pte

With this patch:
UsmMemoryAllocation(api=l0 type=Host size=4KB) 91.7 us
UsmMemoryAllocation(api=l0 type=Host size=1GB) 89486.5 us
91.86%  api_overhead_be [kernel.kallsyms [k] clear_page_erms
1.81%  api_overhead_be  [kernel.kallsyms [k] pages_are_mergeable
0.99%  api_overhead_be  [kernel.kallsyms [k] get_page_from_freelist
0.63%  api_overhead_be  [kernel.kallsyms [k] __free_pages_ok
0.50%  api_overhead_be  [kernel.kallsyms [k] __lock_acquire

For larger memory the delta is very low so it is likely worth
doing gpu based system page clear that can be reconsidered in the
future.

This reverts commit 23683061805be368c8d1c7e7ff52abc470cac275 with
minor conflict fixes.

Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
---
 drivers/gpu/drm/xe/xe_bo.c           | 26 ++------------------------
 drivers/gpu/drm/xe/xe_device_types.h |  2 --
 drivers/gpu/drm/xe/xe_ttm_sys_mgr.c  | 12 ------------
 3 files changed, 2 insertions(+), 38 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
index 24701272e3af..fd4b2b2dfd8d 100644
--- a/drivers/gpu/drm/xe/xe_bo.c
+++ b/drivers/gpu/drm/xe/xe_bo.c
@@ -397,14 +397,6 @@ static struct ttm_tt *xe_ttm_tt_create(struct ttm_buffer_object *ttm_bo,
 		caching = ttm_uncached;
 	}
 
-	/*
-	 * If the device can support gpu clear system pages then set proper ttm
-	 * flag. Zeroed pages are only required for ttm_bo_type_device so
-	 * unwanted data is not leaked to userspace.
-	 */
-	if (ttm_bo->type == ttm_bo_type_device && xe->mem.gpu_page_clear_sys)
-		page_flags |= TTM_TT_FLAG_CLEARED_ON_FREE;
-
 	/* compression is not allowed for cached BO so ccs clear can be skipped. */
 	tt->skip_ccs_clear = caching == ttm_cached;
 	err = ttm_tt_init(&tt->ttm, &bo->ttm, page_flags, caching, extra_pages);
@@ -428,10 +420,6 @@ static int xe_ttm_tt_populate(struct ttm_device *ttm_dev, struct ttm_tt *tt,
 	if (tt->page_flags & TTM_TT_FLAG_EXTERNAL)
 		return 0;
 
-	/* Clear TTM_TT_FLAG_ZERO_ALLOC when GPU is set to clear system pages */
-	if (tt->page_flags & TTM_TT_FLAG_CLEARED_ON_FREE)
-		tt->page_flags &= ~TTM_TT_FLAG_ZERO_ALLOC;
-
 	err = ttm_pool_alloc(&ttm_dev->pool, tt, ctx);
 	if (err)
 		return err;
@@ -677,16 +665,8 @@ static int xe_bo_move(struct ttm_buffer_object *ttm_bo, bool evict,
 	bool handle_system_ccs = (!IS_DGFX(xe) && xe_bo_needs_ccs_pages(bo) &&
 				  ttm && ttm_tt_is_populated(ttm) &&
 				  !xe_tt->skip_ccs_clear) ? true : false;
-	bool clear_system_pages;
 	int ret = 0;
 
-	/*
-	 * Clear TTM_TT_FLAG_CLEARED_ON_FREE on bo creation path when
-	 * moving to system as the bo doesn't have dma_mapping.
-	 */
-	if (!old_mem && ttm && !ttm_tt_is_populated(ttm))
-		ttm->page_flags &= ~TTM_TT_FLAG_CLEARED_ON_FREE;
-
 	/* Bo creation path, moving to system or TT. */
 	if ((!old_mem && ttm) && !handle_system_ccs) {
 		if (new_mem->mem_type == XE_PL_TT)
@@ -709,10 +689,8 @@ static int xe_bo_move(struct ttm_buffer_object *ttm_bo, bool evict,
 	move_lacks_source = handle_system_ccs ? (!bo->ccs_cleared)  :
 						(!mem_type_is_vram(old_mem_type) && !tt_has_data);
 
-	clear_system_pages = ttm && (ttm->page_flags & TTM_TT_FLAG_CLEARED_ON_FREE);
 	needs_clear = (ttm && ttm->page_flags & TTM_TT_FLAG_ZERO_ALLOC) ||
-		(!ttm && ttm_bo->type == ttm_bo_type_device) ||
-		clear_system_pages;
+		(!ttm && ttm_bo->type == ttm_bo_type_device);
 
 	if (new_mem->mem_type == XE_PL_TT) {
 		ret = xe_tt_map_sg(ttm);
@@ -824,7 +802,7 @@ static int xe_bo_move(struct ttm_buffer_object *ttm_bo, bool evict,
 		if (move_lacks_source) {
 			u32 flags = 0;
 
-			if (mem_type_is_vram(new_mem->mem_type) || clear_system_pages)
+			if (mem_type_is_vram(new_mem->mem_type))
 				flags |= XE_MIGRATE_CLEAR_FLAG_FULL;
 			else if (handle_system_ccs)
 				flags |= XE_MIGRATE_CLEAR_FLAG_CCS_DATA;
diff --git a/drivers/gpu/drm/xe/xe_device_types.h b/drivers/gpu/drm/xe/xe_device_types.h
index 4ecd620921a3..e73fb0c23932 100644
--- a/drivers/gpu/drm/xe/xe_device_types.h
+++ b/drivers/gpu/drm/xe/xe_device_types.h
@@ -333,8 +333,6 @@ struct xe_device {
 		struct xe_mem_region vram;
 		/** @mem.sys_mgr: system TTM manager */
 		struct ttm_resource_manager sys_mgr;
-		/** @mem.gpu_page_clear_sys: clear system pages offloaded to GPU */
-		bool gpu_page_clear_sys;
 	} mem;
 
 	/** @sriov: device level virtualization data */
diff --git a/drivers/gpu/drm/xe/xe_ttm_sys_mgr.c b/drivers/gpu/drm/xe/xe_ttm_sys_mgr.c
index e0ac20f20758..9844a8edbfe1 100644
--- a/drivers/gpu/drm/xe/xe_ttm_sys_mgr.c
+++ b/drivers/gpu/drm/xe/xe_ttm_sys_mgr.c
@@ -117,17 +117,5 @@ int xe_ttm_sys_mgr_init(struct xe_device *xe)
 	ttm_resource_manager_init(man, &xe->ttm, gtt_size >> PAGE_SHIFT);
 	ttm_set_driver_manager(&xe->ttm, XE_PL_TT, man);
 	ttm_resource_manager_set_used(man, true);
-
-	/*
-	 * On iGFX device with flat CCS, we clear CCS metadata, let's extend that
-	 * and use GPU to clear pages as well.
-	 *
-	 * Disable this when init_on_free and/or init_on_alloc is on to avoid double
-	 * zeroing pages with CPU and GPU.
-	 */
-	if (xe_device_has_flat_ccs(xe) && !IS_DGFX(xe) &&
-	    !want_init_on_alloc(GFP_USER) && !want_init_on_free())
-		xe->mem.gpu_page_clear_sys = true;
-
 	return drmm_add_action_or_reset(&xe->drm, ttm_sys_mgr_fini, xe);
 }
-- 
2.42.0