[PATCH 7/7] drm/syncobj: Add a fast path to drm_syncobj_array_find
Maíra Canal
mcanal at igalia.com
Mon Mar 24 23:06:47 UTC 2025
Hi Tvrtko,
Some nits inline, mostly personal comments. In any case,
Reviewed-by: Maíra Canal <mcanal at igalia.com>
On 18/03/25 12:54, 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.
>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at igalia.com>
> ---
> drivers/gpu/drm/drm_syncobj.c | 53 +++++++++++++++++++++++++++--------
> 1 file changed, 41 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
> index 94932b89298f..233bdef53c87 100644
> --- a/drivers/gpu/drm/drm_syncobj.c
> +++ b/drivers/gpu/drm/drm_syncobj.c
> @@ -1223,6 +1223,8 @@ 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;
> @@ -1232,9 +1234,13 @@ 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) {
I believe it's worth adding a comment mentioning that using the stack
syncobj is a fast-path that covers most cases.
> + syncobjs = kmalloc_array(count, sizeof(*syncobjs), GFP_KERNEL);
> + if (!syncobjs)
> + return -ENOMEM;
> + } else {
> + syncobjs = stack_syncobjs;
> + }
>
> for (i = 0; i < count; i++) {
> u64 handle;
> @@ -1260,25 +1266,31 @@ static int drm_syncobj_array_find(struct drm_file *file_private,
> drm_syncobj_put(syncobjs[i]);
> i--;
> }
> - kfree(syncobjs);
> +
> + if (syncobjs != stack_syncobjs)
Again, I have a slight preference to make `syncobjs = NULL` and avoid
this if condition. But it's just a personal preference.
> + kfree(syncobjs);
>
> return ret;
> }
>
> static void drm_syncobj_array_free(struct drm_syncobj **syncobjs,
> - uint32_t count)
> + uint32_t count,
> + struct drm_syncobj **stack_syncobjs)
IMO, I think the order `syncobjs, stack_syncobjs, count` is a bit more
intuitive.
> {
> uint32_t i;
>
> for (i = 0; i < count; i++)
> drm_syncobj_put(syncobjs[i]);
> - kfree(syncobjs);
> +
> + if (syncobjs != stack_syncobjs)
> + kfree(syncobjs);
> }
>
> int
> drm_syncobj_wait_ioctl(struct drm_device *dev, void *data,
> struct drm_file *file_private)
> {
> + struct drm_syncobj *stack_syncobjs[4];
> struct drm_syncobj_wait *args = data;
> ktime_t deadline, *pdeadline = NULL;
> u32 count = args->count_handles;
> @@ -1304,6 +1316,8 @@ 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;
> @@ -1321,7 +1335,7 @@ drm_syncobj_wait_ioctl(struct drm_device *dev, void *data,
> &first,
> pdeadline);
>
> - drm_syncobj_array_free(syncobjs, count);
> + drm_syncobj_array_free(syncobjs, count, stack_syncobjs);
>
> if (timeout < 0)
> return timeout;
> @@ -1336,6 +1350,7 @@ drm_syncobj_timeline_wait_ioctl(struct drm_device *dev, void *data,
> struct drm_file *file_private)
> {
> struct drm_syncobj_timeline_wait *args = data;
> + struct drm_syncobj *stack_syncobjs[4];
Zero initialize it?
Best Regards,
- Maíra
> ktime_t deadline, *pdeadline = NULL;
> u32 count = args->count_handles;
> struct drm_syncobj **syncobjs;
> @@ -1361,6 +1376,8 @@ 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;
> @@ -1378,7 +1395,7 @@ 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, stack_syncobjs);
>
> if (timeout < 0)
> return timeout;
> @@ -1496,6 +1513,7 @@ drm_syncobj_reset_ioctl(struct drm_device *dev, void *data,
> struct drm_file *file_private)
> {
> struct drm_syncobj_array *args = data;
> + struct drm_syncobj *stack_syncobjs[4];
> struct drm_syncobj **syncobjs;
> uint32_t i;
> int ret;
> @@ -1512,6 +1530,8 @@ 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;
> @@ -1519,7 +1539,7 @@ 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, stack_syncobjs);
>
> return 0;
> }
> @@ -1529,6 +1549,7 @@ drm_syncobj_signal_ioctl(struct drm_device *dev, void *data,
> struct drm_file *file_private)
> {
> struct drm_syncobj_array *args = data;
> + struct drm_syncobj *stack_syncobjs[4];
> struct drm_syncobj **syncobjs;
> uint32_t i;
> int ret;
> @@ -1545,6 +1566,8 @@ 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;
> @@ -1555,7 +1578,7 @@ 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, stack_syncobjs);
>
> return ret;
> }
> @@ -1567,6 +1590,7 @@ drm_syncobj_timeline_signal_ioctl(struct drm_device *dev, void *data,
> 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 *stack_syncobjs[4];
> struct drm_syncobj **syncobjs;
> struct dma_fence_chain **chains;
> int ret;
> @@ -1586,6 +1610,8 @@ 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;
> @@ -1622,7 +1648,7 @@ 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, stack_syncobjs);
>
> return ret;
> }
> @@ -1631,6 +1657,7 @@ int drm_syncobj_query_ioctl(struct drm_device *dev, void *data,
> struct drm_file *file_private)
> {
> struct drm_syncobj_timeline_array *args = data;
> + struct drm_syncobj *stack_syncobjs[4];
> struct drm_syncobj **syncobjs;
> uint64_t __user *points = u64_to_user_ptr(args->points);
> uint32_t i;
> @@ -1651,6 +1678,8 @@ 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;
> @@ -1694,7 +1723,7 @@ int drm_syncobj_query_ioctl(struct drm_device *dev, void *data,
> break;
> }
> }
> - drm_syncobj_array_free(syncobjs, args->count_handles);
> + drm_syncobj_array_free(syncobjs, args->count_handles, stack_syncobjs);
>
> return ret;
> }
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