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Wed, 11 Jun 2025 14:15:11 +0000 Message-ID: <4211da66-9bed-41ee-a596-046bbc0906e0@amd.com> Date: Wed, 11 Jun 2025 16:15:07 +0200 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 4/6] drm/syncobj: Avoid temporary allocation in drm_syncobj_timeline_signal_ioctl To: Tvrtko Ursulin , dri-devel@lists.freedesktop.org Cc: kernel-dev@igalia.com, amd-gfx@lists.freedesktop.org, intel-xe@lists.freedesktop.org, =?UTF-8?Q?Michel_D=C3=A4nzer?= , =?UTF-8?Q?Ma=C3=ADra_Canal?= References: <20250611140057.27259-1-tvrtko.ursulin@igalia.com> <20250611140057.27259-5-tvrtko.ursulin@igalia.com> Content-Language: en-US From: =?UTF-8?Q?Christian_K=C3=B6nig?= In-Reply-To: <20250611140057.27259-5-tvrtko.ursulin@igalia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: BLAPR03CA0096.namprd03.prod.outlook.com (2603:10b6:208:32a::11) To PH7PR12MB5685.namprd12.prod.outlook.com (2603:10b6:510:13c::22) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH7PR12MB5685:EE_|PH7PR12MB7282:EE_ X-MS-Office365-Filtering-Correlation-Id: 44099f8d-0a19-4dc2-cad3-08dda8f2609d X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|376014|7053199007; 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The problem with that is that calling copy_from_user multiple times is really inefficient. So that improves performance with few entries and decreases performance with many entries. Not sure if having many entries is really a valid use case here. Regards, Christian. > > The only new complication is to unwind unused fence chains on the error > path, but even that code was already present in the function. > > Signed-off-by: Tvrtko Ursulin > Reviewed-by: Maíra Canal #v1 > --- > v2: > * Change back to copy_from_user due 32-bit ARM not implementing 64-bit > get_user. > > v3: > * Fix argument order mixup. > --- > drivers/gpu/drm/drm_syncobj.c | 43 ++++++++++++++--------------------- > 1 file changed, 17 insertions(+), 26 deletions(-) > > diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c > index 497009fc66f8..9968d9429d90 100644 > --- a/drivers/gpu/drm/drm_syncobj.c > +++ b/drivers/gpu/drm/drm_syncobj.c > @@ -1579,10 +1579,10 @@ drm_syncobj_timeline_signal_ioctl(struct drm_device *dev, void *data, > struct drm_file *file_private) > { > struct drm_syncobj_timeline_array *args = data; > + uint64_t __user *points = u64_to_user_ptr(args->points); > + uint32_t i, j, count = args->count_handles; > struct drm_syncobj **syncobjs; > struct dma_fence_chain **chains; > - uint64_t *points; > - uint32_t i, j; > int ret; > > if (!drm_core_check_feature(dev, DRIVER_SYNCOBJ_TIMELINE)) > @@ -1596,31 +1596,17 @@ drm_syncobj_timeline_signal_ioctl(struct drm_device *dev, void *data, > > ret = drm_syncobj_array_find(file_private, > u64_to_user_ptr(args->handles), > - args->count_handles, > + count, > &syncobjs); > if (ret < 0) > return ret; > > - points = kmalloc_array(args->count_handles, sizeof(*points), > - GFP_KERNEL); > - if (!points) { > - ret = -ENOMEM; > - goto out; > - } > - if (!u64_to_user_ptr(args->points)) { > - memset(points, 0, args->count_handles * sizeof(uint64_t)); > - } else if (copy_from_user(points, u64_to_user_ptr(args->points), > - sizeof(uint64_t) * args->count_handles)) { > - ret = -EFAULT; > - goto err_points; > - } > - > - chains = kmalloc_array(args->count_handles, sizeof(void *), GFP_KERNEL); > + chains = kmalloc_array(count, sizeof(void *), GFP_KERNEL); > if (!chains) { > ret = -ENOMEM; > - goto err_points; > + goto out; > } > - for (i = 0; i < args->count_handles; i++) { > + for (i = 0; i < count; i++) { > chains[i] = dma_fence_chain_alloc(); > if (!chains[i]) { > for (j = 0; j < i; j++) > @@ -1630,19 +1616,24 @@ drm_syncobj_timeline_signal_ioctl(struct drm_device *dev, void *data, > } > } > > - for (i = 0; i < args->count_handles; i++) { > + for (i = 0; i < count; i++) { > struct dma_fence *fence = dma_fence_get_stub(); > + u64 point = 0; > > - drm_syncobj_add_point(syncobjs[i], chains[i], > - fence, points[i]); > + if (points && copy_from_user(&point, points++, sizeof(point))) { > + ret = -EFAULT; > + for (j = i; j < count; j++) > + dma_fence_chain_free(chains[j]); > + goto err_chains; > + } > + > + drm_syncobj_add_point(syncobjs[i], chains[i], fence, point); > dma_fence_put(fence); > } > err_chains: > kfree(chains); > -err_points: > - kfree(points); > out: > - drm_syncobj_array_free(syncobjs, args->count_handles); > + drm_syncobj_array_free(syncobjs, count); > > return ret; > }