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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 v18 21/26] drm/shmem-helper: Optimize unlocked get_pages_sgt()
Date:   Mon, 30 Oct 2023 02:02:00 +0300
Message-ID: <20231029230205.93277-22-dmitry.osipenko@collabora.com>
In-Reply-To: <20231029230205.93277-1-dmitry.osipenko@collabora.com>
References: <20231029230205.93277-1-dmitry.osipenko@collabora.com>
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SGT isn't refcounted. Once SGT pointer has been obtained, it remains the
same for both locked and unlocked get_pages_sgt(). Return cached SGT
directly without taking a potentially expensive lock.

Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
---
 drivers/gpu/drm/drm_gem_shmem_helper.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 560ce565f376..6dd087f19ea3 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -955,6 +955,9 @@ struct sg_table *drm_gem_shmem_get_pages_sgt(struct drm_gem_shmem_object *shmem)
 	drm_WARN_ON(obj->dev, drm_gem_shmem_is_evictable(shmem));
 	drm_WARN_ON(obj->dev, drm_gem_shmem_is_purgeable(shmem));
 
+	if (shmem->sgt)
+		return shmem->sgt;
+
 	ret = dma_resv_lock_interruptible(shmem->base.resv, NULL);
 	if (ret)
 		return ERR_PTR(ret);
-- 
2.41.0