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From:   Dmitry Osipenko <dmitry.osipenko@collabora.com>
To:     David Airlie <airlied@gmail.com>,
        Gerd Hoffmann <kraxel@redhat.com>,
        Gurchetan Singh <gurchetansingh@chromium.org>,
        Chia-I Wu <olvaffe@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        =?UTF-8?q?Christian=20K=C3=B6nig?= <christian.koenig@amd.com>,
        Qiang Yu <yuq825@gmail.com>,
        Steven Price <steven.price@arm.com>,
        Boris Brezillon <boris.brezillon@collabora.com>,
        Emma Anholt <emma@anholt.net>, Melissa Wen <mwen@igalia.com>
Cc:     dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        kernel@collabora.com, virtualization@lists.linux-foundation.org
Subject: [PATCH v17 07/18] drm/shmem-helper: Use refcount_t for pages_use_count
Date:   Fri, 15 Sep 2023 02:27:10 +0300
Message-ID: <20230914232721.408581-8-dmitry.osipenko@collabora.com>
In-Reply-To: <20230914232721.408581-1-dmitry.osipenko@collabora.com>
References: <20230914232721.408581-1-dmitry.osipenko@collabora.com>
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Use atomic refcount_t helper for pages_use_count to optimize pin/unpin
functions by skipping reservation locking while GEM's pin refcount > 1.

Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
---
 drivers/gpu/drm/drm_gem_shmem_helper.c  | 33 +++++++++++--------------
 drivers/gpu/drm/lima/lima_gem.c         |  2 +-
 drivers/gpu/drm/panfrost/panfrost_mmu.c |  2 +-
 include/drm/drm_gem_shmem_helper.h      |  2 +-
 4 files changed, 18 insertions(+), 21 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 286f0ca51309..e9d9fbd52b34 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -155,7 +155,7 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
 		if (shmem->pages)
 			drm_gem_shmem_put_pages_locked(shmem);
 
-		drm_WARN_ON(obj->dev, shmem->pages_use_count);
+		drm_WARN_ON(obj->dev, refcount_read(&shmem->pages_use_count));
 
 		dma_resv_unlock(shmem->base.resv);
 	}
@@ -172,14 +172,13 @@ static int drm_gem_shmem_get_pages_locked(struct drm_gem_shmem_object *shmem)
 
 	dma_resv_assert_held(shmem->base.resv);
 
-	if (shmem->pages_use_count++ > 0)
+	if (refcount_inc_not_zero(&shmem->pages_use_count))
 		return 0;
 
 	pages = drm_gem_get_pages(obj);
 	if (IS_ERR(pages)) {
 		drm_dbg_kms(obj->dev, "Failed to get pages (%ld)\n",
 			    PTR_ERR(pages));
-		shmem->pages_use_count = 0;
 		return PTR_ERR(pages);
 	}
 
@@ -195,6 +194,8 @@ static int drm_gem_shmem_get_pages_locked(struct drm_gem_shmem_object *shmem)
 
 	shmem->pages = pages;
 
+	refcount_set(&shmem->pages_use_count, 1);
+
 	return 0;
 }
 
@@ -210,21 +211,17 @@ void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem)
 
 	dma_resv_assert_held(shmem->base.resv);
 
-	if (drm_WARN_ON_ONCE(obj->dev, !shmem->pages_use_count))
-		return;
-
-	if (--shmem->pages_use_count > 0)
-		return;
-
+	if (refcount_dec_and_test(&shmem->pages_use_count)) {
 #ifdef CONFIG_X86
-	if (shmem->map_wc)
-		set_pages_array_wb(shmem->pages, obj->size >> PAGE_SHIFT);
+		if (shmem->map_wc)
+			set_pages_array_wb(shmem->pages, obj->size >> PAGE_SHIFT);
 #endif
 
-	drm_gem_put_pages(obj, shmem->pages,
-			  shmem->pages_mark_dirty_on_put,
-			  shmem->pages_mark_accessed_on_put);
-	shmem->pages = NULL;
+		drm_gem_put_pages(obj, shmem->pages,
+				  shmem->pages_mark_dirty_on_put,
+				  shmem->pages_mark_accessed_on_put);
+		shmem->pages = NULL;
+	}
 }
 EXPORT_SYMBOL_GPL(drm_gem_shmem_put_pages_locked);
 
@@ -551,8 +548,8 @@ static void drm_gem_shmem_vm_open(struct vm_area_struct *vma)
 	 * mmap'd, vm_open() just grabs an additional reference for the new
 	 * mm the vma is getting copied into (ie. on fork()).
 	 */
-	if (!drm_WARN_ON_ONCE(obj->dev, !shmem->pages_use_count))
-		shmem->pages_use_count++;
+	drm_WARN_ON_ONCE(obj->dev,
+			 !refcount_inc_not_zero(&shmem->pages_use_count));
 
 	dma_resv_unlock(shmem->base.resv);
 
@@ -640,7 +637,7 @@ void drm_gem_shmem_print_info(const struct drm_gem_shmem_object *shmem,
 		return;
 
 	drm_printf_indent(p, indent, "pages_pin_count=%u\n", refcount_read(&shmem->pages_pin_count));
-	drm_printf_indent(p, indent, "pages_use_count=%u\n", shmem->pages_use_count);
+	drm_printf_indent(p, indent, "pages_use_count=%u\n", refcount_read(&shmem->pages_use_count));
 	drm_printf_indent(p, indent, "vmap_use_count=%u\n", shmem->vmap_use_count);
 	drm_printf_indent(p, indent, "vaddr=%p\n", shmem->vaddr);
 }
diff --git a/drivers/gpu/drm/lima/lima_gem.c b/drivers/gpu/drm/lima/lima_gem.c
index 62d4a409faa8..988e74f67465 100644
--- a/drivers/gpu/drm/lima/lima_gem.c
+++ b/drivers/gpu/drm/lima/lima_gem.c
@@ -47,7 +47,7 @@ int lima_heap_alloc(struct lima_bo *bo, struct lima_vm *vm)
 		}
 
 		bo->base.pages = pages;
-		bo->base.pages_use_count = 1;
+		refcount_set(&bo->base.pages_use_count, 1);
 
 		mapping_set_unevictable(mapping);
 	}
diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c
index 7771769f0ce0..a91252053aa3 100644
--- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
+++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
@@ -487,7 +487,7 @@ static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as,
 			goto err_unlock;
 		}
 		bo->base.pages = pages;
-		bo->base.pages_use_count = 1;
+		refcount_set(&bo->base.pages_use_count, 1);
 	} else {
 		pages = bo->base.pages;
 		if (pages[page_offset]) {
diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
index 268b3127d150..3947f5c6bff7 100644
--- a/include/drm/drm_gem_shmem_helper.h
+++ b/include/drm/drm_gem_shmem_helper.h
@@ -37,7 +37,7 @@ struct drm_gem_shmem_object {
 	 * Reference count on the pages table.
 	 * The pages are put when the count reaches zero.
 	 */
-	unsigned int pages_use_count;
+	refcount_t pages_use_count;
 
 	/**
 	 * @pages_pin_count:
-- 
2.41.0