[PATCH v5 6/6] drm/syncobj: Add a fast path to drm_syncobj_array_find
Christian König
christian.koenig at amd.com
Wed Jun 11 14:21:39 UTC 2025
On 6/11/25 16:00, Tvrtko Ursulin wrote:
> Running the Cyberpunk 2077 benchmark we can observe that the lookup helper
> is relatively hot, but the 97% of the calls are for a single object. (~3%
> for two points, and never more than three points. While a more trivial
> workload like vkmark under Plasma is even more skewed to single point
> lookups.)
>
> Therefore lets add a fast path to bypass the kmalloc_array/kfree and use a
> pre-allocated stack array for those cases.
Have you considered using memdup_user()? That's using a separate bucket IIRC and might give similar performance.
If that is still not sufficient I'm really wondering if we shouldn't have a macro for doing this. It's a really common use case as far as I can see.
Regards,
Christian.
>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at igalia.com>
> Reviewed-by: Maíra Canal <mcanal at igalia.com>
> ---
> v2:
> * Added comments describing how the fast path arrays were sized.
> * Make container freeing criteria clearer by using a boolean.
> ---
> drivers/gpu/drm/drm_syncobj.c | 56 +++++++++++++++++++++++++++--------
> 1 file changed, 44 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
> index be5905dca87f..65c301852f0d 100644
> --- a/drivers/gpu/drm/drm_syncobj.c
> +++ b/drivers/gpu/drm/drm_syncobj.c
> @@ -1259,6 +1259,8 @@ EXPORT_SYMBOL(drm_timeout_abs_to_jiffies);
> static int drm_syncobj_array_find(struct drm_file *file_private,
> u32 __user *handles,
> uint32_t count,
> + struct drm_syncobj **stack_syncobjs,
> + u32 stack_count,
> struct drm_syncobj ***syncobjs_out)
> {
> struct drm_syncobj **syncobjs;
> @@ -1268,9 +1270,13 @@ static int drm_syncobj_array_find(struct drm_file *file_private,
> if (!access_ok(handles, count * sizeof(*handles)))
> return -EFAULT;
>
> - syncobjs = kmalloc_array(count, sizeof(*syncobjs), GFP_KERNEL);
> - if (!syncobjs)
> - return -ENOMEM;
> + if (count > stack_count) {
> + syncobjs = kmalloc_array(count, sizeof(*syncobjs), GFP_KERNEL);
> + if (!syncobjs)
> + return -ENOMEM;
> + } else {
> + syncobjs = stack_syncobjs;
> + }
>
> for (i = 0; i < count; i++) {
> u32 handle;
> @@ -1292,25 +1298,31 @@ static int drm_syncobj_array_find(struct drm_file *file_private,
> err_put_syncobjs:
> while (i-- > 0)
> drm_syncobj_put(syncobjs[i]);
> - kfree(syncobjs);
> +
> + if (syncobjs != stack_syncobjs)
> + kfree(syncobjs);
>
> return ret;
> }
>
> static void drm_syncobj_array_free(struct drm_syncobj **syncobjs,
> - uint32_t count)
> + uint32_t count,
> + bool free_container)
> {
> uint32_t i;
>
> for (i = 0; i < count; i++)
> drm_syncobj_put(syncobjs[i]);
> - kfree(syncobjs);
> +
> + if (free_container)
> + kfree(syncobjs);
> }
>
> int
> drm_syncobj_wait_ioctl(struct drm_device *dev, void *data,
> struct drm_file *file_private)
> {
> + struct drm_syncobj *stack_syncobjs[DRM_SYNCOBJ_FAST_PATH_ENTRIES];
> struct drm_syncobj_wait *args = data;
> ktime_t deadline, *pdeadline = NULL;
> u32 count = args->count_handles;
> @@ -1336,6 +1348,8 @@ drm_syncobj_wait_ioctl(struct drm_device *dev, void *data,
> ret = drm_syncobj_array_find(file_private,
> u64_to_user_ptr(args->handles),
> count,
> + stack_syncobjs,
> + ARRAY_SIZE(stack_syncobjs),
> &syncobjs);
> if (ret < 0)
> return ret;
> @@ -1354,7 +1368,7 @@ drm_syncobj_wait_ioctl(struct drm_device *dev, void *data,
> &first,
> pdeadline);
>
> - drm_syncobj_array_free(syncobjs, count);
> + drm_syncobj_array_free(syncobjs, count, syncobjs != stack_syncobjs);
>
> if (timeout < 0)
> return timeout;
> @@ -1368,6 +1382,7 @@ int
> drm_syncobj_timeline_wait_ioctl(struct drm_device *dev, void *data,
> struct drm_file *file_private)
> {
> + struct drm_syncobj *stack_syncobjs[DRM_SYNCOBJ_FAST_PATH_ENTRIES];
> struct drm_syncobj_timeline_wait *args = data;
> ktime_t deadline, *pdeadline = NULL;
> u32 count = args->count_handles;
> @@ -1394,6 +1409,8 @@ drm_syncobj_timeline_wait_ioctl(struct drm_device *dev, void *data,
> ret = drm_syncobj_array_find(file_private,
> u64_to_user_ptr(args->handles),
> count,
> + stack_syncobjs,
> + ARRAY_SIZE(stack_syncobjs),
> &syncobjs);
> if (ret < 0)
> return ret;
> @@ -1412,7 +1429,7 @@ drm_syncobj_timeline_wait_ioctl(struct drm_device *dev, void *data,
> &first,
> pdeadline);
>
> - drm_syncobj_array_free(syncobjs, count);
> + drm_syncobj_array_free(syncobjs, count, syncobjs != stack_syncobjs);
>
> if (timeout < 0)
> return timeout;
> @@ -1529,6 +1546,7 @@ int
> drm_syncobj_reset_ioctl(struct drm_device *dev, void *data,
> struct drm_file *file_private)
> {
> + struct drm_syncobj *stack_syncobjs[DRM_SYNCOBJ_FAST_PATH_ENTRIES];
> struct drm_syncobj_array *args = data;
> struct drm_syncobj **syncobjs;
> uint32_t i;
> @@ -1546,6 +1564,8 @@ drm_syncobj_reset_ioctl(struct drm_device *dev, void *data,
> ret = drm_syncobj_array_find(file_private,
> u64_to_user_ptr(args->handles),
> args->count_handles,
> + stack_syncobjs,
> + ARRAY_SIZE(stack_syncobjs),
> &syncobjs);
> if (ret < 0)
> return ret;
> @@ -1553,7 +1573,8 @@ drm_syncobj_reset_ioctl(struct drm_device *dev, void *data,
> for (i = 0; i < args->count_handles; i++)
> drm_syncobj_replace_fence(syncobjs[i], NULL);
>
> - drm_syncobj_array_free(syncobjs, args->count_handles);
> + drm_syncobj_array_free(syncobjs, args->count_handles,
> + syncobjs != stack_syncobjs);
>
> return 0;
> }
> @@ -1562,6 +1583,7 @@ int
> drm_syncobj_signal_ioctl(struct drm_device *dev, void *data,
> struct drm_file *file_private)
> {
> + struct drm_syncobj *stack_syncobjs[DRM_SYNCOBJ_FAST_PATH_ENTRIES];
> struct drm_syncobj_array *args = data;
> struct drm_syncobj **syncobjs;
> uint32_t i;
> @@ -1579,6 +1601,8 @@ drm_syncobj_signal_ioctl(struct drm_device *dev, void *data,
> ret = drm_syncobj_array_find(file_private,
> u64_to_user_ptr(args->handles),
> args->count_handles,
> + stack_syncobjs,
> + ARRAY_SIZE(stack_syncobjs),
> &syncobjs);
> if (ret < 0)
> return ret;
> @@ -1589,7 +1613,8 @@ drm_syncobj_signal_ioctl(struct drm_device *dev, void *data,
> break;
> }
>
> - drm_syncobj_array_free(syncobjs, args->count_handles);
> + drm_syncobj_array_free(syncobjs, args->count_handles,
> + syncobjs != stack_syncobjs);
>
> return ret;
> }
> @@ -1598,6 +1623,7 @@ int
> drm_syncobj_timeline_signal_ioctl(struct drm_device *dev, void *data,
> struct drm_file *file_private)
> {
> + struct drm_syncobj *stack_syncobjs[DRM_SYNCOBJ_FAST_PATH_ENTRIES];
> 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;
> @@ -1617,6 +1643,8 @@ drm_syncobj_timeline_signal_ioctl(struct drm_device *dev, void *data,
> ret = drm_syncobj_array_find(file_private,
> u64_to_user_ptr(args->handles),
> count,
> + stack_syncobjs,
> + ARRAY_SIZE(stack_syncobjs),
> &syncobjs);
> if (ret < 0)
> return ret;
> @@ -1653,7 +1681,7 @@ drm_syncobj_timeline_signal_ioctl(struct drm_device *dev, void *data,
> err_chains:
> kfree(chains);
> out:
> - drm_syncobj_array_free(syncobjs, count);
> + drm_syncobj_array_free(syncobjs, count, syncobjs != stack_syncobjs);
>
> return ret;
> }
> @@ -1661,6 +1689,7 @@ drm_syncobj_timeline_signal_ioctl(struct drm_device *dev, void *data,
> int drm_syncobj_query_ioctl(struct drm_device *dev, void *data,
> struct drm_file *file_private)
> {
> + struct drm_syncobj *stack_syncobjs[DRM_SYNCOBJ_FAST_PATH_ENTRIES];
> struct drm_syncobj_timeline_array *args = data;
> struct drm_syncobj **syncobjs;
> uint64_t __user *points = u64_to_user_ptr(args->points);
> @@ -1679,6 +1708,8 @@ int drm_syncobj_query_ioctl(struct drm_device *dev, void *data,
> ret = drm_syncobj_array_find(file_private,
> u64_to_user_ptr(args->handles),
> args->count_handles,
> + stack_syncobjs,
> + ARRAY_SIZE(stack_syncobjs),
> &syncobjs);
> if (ret < 0)
> return ret;
> @@ -1722,7 +1753,8 @@ int drm_syncobj_query_ioctl(struct drm_device *dev, void *data,
> if (ret)
> break;
> }
> - drm_syncobj_array_free(syncobjs, args->count_handles);
> + drm_syncobj_array_free(syncobjs, args->count_handles,
> + syncobjs != stack_syncobjs);
>
> return ret;
> }
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