[PATCH v3 2/2] drm/xe/lnl: Offload system clear page activity to GPU

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

On LNL because of flat CCS, driver creates a migrate job to clear
CCS meta data. Extend that to also clear system pages using GPU.
Inform TTM to allocate pages without __GFP_ZERO to avoid double page
clearing by clearing out TTM_TT_FLAG_ZERO_ALLOC flag and set
TTM_TT_FLAG_CLEARED_ON_FREE while freeing to skip ttm pool's
clearn-on-free as XE now takes care of clearing pages.

To test the patch, I created a small test that tries to submit a job
after binding various sizes of buffer which shows good gains for larger
buffer. For lower buffer sizes, the result is not very reliable as the
results vary a lot.

With the patch
sudo  ~/igt-gpu-tools/build/tests/xe_exec_store --run basic-store-benchmark
IGT-Version: 1.28-g2ed908c0b (x86_64) (Linux: 6.10.0-rc2-xe+ x86_64)
Using IGT_SRANDOM=1719237905 for randomisation
Opened device: /dev/dri/card0
Starting subtest: basic-store-benchmark
Starting dynamic subtest: WC
Dynamic subtest WC: SUCCESS (0.000s)
Time taken for size SZ_4K: 9493 us
Time taken for size SZ_2M: 5503 us
Time taken for size SZ_64M: 13016 us
Time taken for size SZ_128M: 29464 us
Time taken for size SZ_256M: 38408 us
Time taken for size SZ_1G: 148758 us
Starting dynamic subtest: WB
Dynamic subtest WB: SUCCESS (0.000s)
Time taken for size SZ_4K: 3889 us
Time taken for size SZ_2M: 6091 us
Time taken for size SZ_64M: 20920 us
Time taken for size SZ_128M: 32394 us
Time taken for size SZ_256M: 61710 us
Time taken for size SZ_1G: 215437 us
Subtest basic-store-benchmark: SUCCESS (0.589s)

With the patch:
sudo  ~/igt-gpu-tools/build/tests/xe_exec_store --run basic-store-benchmark
IGT-Version: 1.28-g2ed908c0b (x86_64) (Linux: 6.10.0-rc2-xe+ x86_64)
Using IGT_SRANDOM=1719238062 for randomisation
Opened device: /dev/dri/card0
Starting subtest: basic-store-benchmark
Starting dynamic subtest: WC
Dynamic subtest WC: SUCCESS (0.000s)
Time taken for size SZ_4K: 11803 us
Time taken for size SZ_2M: 4237 us
Time taken for size SZ_64M: 8649 us
Time taken for size SZ_128M: 14682 us
Time taken for size SZ_256M: 22156 us
Time taken for size SZ_1G: 74457 us
Starting dynamic subtest: WB
Dynamic subtest WB: SUCCESS (0.000s)
Time taken for size SZ_4K: 5129 us
Time taken for size SZ_2M: 12563 us
Time taken for size SZ_64M: 14860 us
Time taken for size SZ_128M: 26064 us
Time taken for size SZ_256M: 47167 us
Time taken for size SZ_1G: 170304 us
Subtest basic-store-benchmark: SUCCESS (0.417s)

With the patch and init_on_alloc=0
sudo  ~/igt-gpu-tools/build/tests/xe_exec_store --run basic-store-benchmark
IGT-Version: 1.28-g2ed908c0b (x86_64) (Linux: 6.10.0-rc2-xe+ x86_64)
Using IGT_SRANDOM=1719238219 for randomisation
Opened device: /dev/dri/card0
Starting subtest: basic-store-benchmark
Starting dynamic subtest: WC
Dynamic subtest WC: SUCCESS (0.000s)
Time taken for size SZ_4K: 4803 us
Time taken for size SZ_2M: 9212 us
Time taken for size SZ_64M: 9643 us
Time taken for size SZ_128M: 13479 us
Time taken for size SZ_256M: 22429 us
Time taken for size SZ_1G: 83110 us
Starting dynamic subtest: WB
Dynamic subtest WB: SUCCESS (0.000s)
Time taken for size SZ_4K: 4003 us
Time taken for size SZ_2M: 4443 us
Time taken for size SZ_64M: 12960 us
Time taken for size SZ_128M: 13741 us
Time taken for size SZ_256M: 26841 us
Time taken for size SZ_1G: 84746 us
Subtest basic-store-benchmark: SUCCESS (0.290s)

v2: Handle regression on dgfx(Himal)
    Update commit message as no ttm API changes needed.
v3: Fix Kunit test.

Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Cc: Matthew Auld <matthew.auld@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           | 11 +++++++++++
 drivers/gpu/drm/xe/xe_device.c       |  7 +++++++
 drivers/gpu/drm/xe/xe_device_types.h |  2 ++
 drivers/gpu/drm/xe/xe_migrate.c      |  5 +++--
 4 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
index 65c696966e96..a9ce4347a7d7 100644
--- a/drivers/gpu/drm/xe/xe_bo.c
+++ b/drivers/gpu/drm/xe/xe_bo.c
@@ -399,6 +399,7 @@ static struct ttm_tt *xe_ttm_tt_create(struct ttm_buffer_object *ttm_bo,
 static int xe_ttm_tt_populate(struct ttm_device *ttm_dev, struct ttm_tt *tt,
 			      struct ttm_operation_ctx *ctx)
 {
+	struct xe_device *xe = ttm_to_xe_device(ttm_dev);
 	int err;
 
 	/*
@@ -408,6 +409,10 @@ 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 pages */
+	if (xe->mem.gpu_page_clear)
+		tt->page_flags &= ~TTM_TT_FLAG_ZERO_ALLOC;
+
 	err = ttm_pool_alloc(&ttm_dev->pool, tt, ctx);
 	if (err)
 		return err;
@@ -417,9 +422,15 @@ static int xe_ttm_tt_populate(struct ttm_device *ttm_dev, struct ttm_tt *tt,
 
 static void xe_ttm_tt_unpopulate(struct ttm_device *ttm_dev, struct ttm_tt *tt)
 {
+	struct xe_device *xe = ttm_to_xe_device(ttm_dev);
+
 	if (tt->page_flags & TTM_TT_FLAG_EXTERNAL)
 		return;
 
+	/* Add TTM_TT_FLAG_CLEARED_ON_FREE when GPU is set to clear pages */
+	if (xe->mem.gpu_page_clear)
+		tt->page_flags |= TTM_TT_FLAG_CLEARED_ON_FREE;
+
 	xe_tt_unmap_sg(tt);
 
 	return ttm_pool_free(&ttm_dev->pool, tt);
diff --git a/drivers/gpu/drm/xe/xe_device.c b/drivers/gpu/drm/xe/xe_device.c
index ca5e8435485a..c9afff1d0734 100644
--- a/drivers/gpu/drm/xe/xe_device.c
+++ b/drivers/gpu/drm/xe/xe_device.c
@@ -636,6 +636,13 @@ int xe_device_probe(struct xe_device *xe)
 	if (err)
 		goto err_irq_shutdown;
 
+	/**
+	 * On iGFX device with flat CCS, we clear CCS metadata, let's extend that
+	 * and use GPU to clear pages as well.
+	 */
+	if (xe_device_has_flat_ccs(xe) && !IS_DGFX(xe))
+		xe->mem.gpu_page_clear = true;
+
 	err = xe_vram_probe(xe);
 	if (err)
 		goto err_irq_shutdown;
diff --git a/drivers/gpu/drm/xe/xe_device_types.h b/drivers/gpu/drm/xe/xe_device_types.h
index c37be471d11c..ece68c6f3668 100644
--- a/drivers/gpu/drm/xe/xe_device_types.h
+++ b/drivers/gpu/drm/xe/xe_device_types.h
@@ -325,6 +325,8 @@ struct xe_device {
 		struct xe_mem_region vram;
 		/** @mem.sys_mgr: system TTM manager */
 		struct ttm_resource_manager sys_mgr;
+		/** @gpu_page_clear: clear pages offloaded to GPU */
+		bool gpu_page_clear;
 	} mem;
 
 	/** @sriov: device level virtualization data */
diff --git a/drivers/gpu/drm/xe/xe_migrate.c b/drivers/gpu/drm/xe/xe_migrate.c
index 05f933787860..61bf3d80e896 100644
--- a/drivers/gpu/drm/xe/xe_migrate.c
+++ b/drivers/gpu/drm/xe/xe_migrate.c
@@ -1003,6 +1003,7 @@ struct dma_fence *xe_migrate_clear(struct xe_migrate *m,
 	struct xe_gt *gt = m->tile->primary_gt;
 	struct xe_device *xe = gt_to_xe(gt);
 	bool clear_system_ccs = (xe_bo_needs_ccs_pages(bo) && !IS_DGFX(xe)) ? true : false;
+	bool clear_on_create = xe->mem.gpu_page_clear || !clear_system_ccs;
 	struct dma_fence *fence = NULL;
 	u64 size = bo->size;
 	struct xe_res_cursor src_it;
@@ -1032,7 +1033,7 @@ struct dma_fence *xe_migrate_clear(struct xe_migrate *m,
 		batch_size = 2 +
 			pte_update_size(m, clear_vram, src, &src_it,
 					&clear_L0, &clear_L0_ofs, &clear_L0_pt,
-					clear_system_ccs ? 0 : emit_clear_cmd_len(gt), 0,
+					!clear_on_create ? 0 : emit_clear_cmd_len(gt), 0,
 					avail_pts);
 
 		if (xe_device_has_flat_ccs(xe))
@@ -1060,7 +1061,7 @@ struct dma_fence *xe_migrate_clear(struct xe_migrate *m,
 		bb->cs[bb->len++] = MI_BATCH_BUFFER_END;
 		update_idx = bb->len;
 
-		if (!clear_system_ccs)
+		if (clear_on_create)
 			emit_clear(gt, bb, clear_L0_ofs, clear_L0, XE_PAGE_SIZE, clear_vram);
 
 		if (xe_device_has_flat_ccs(xe)) {
-- 
2.42.0