On Tue, Oct 22, 2024 at 9:53 AM Christian König
<christian.koenig@xxxxxxx> wrote:
>
> Am 22.10.24 um 18:18 schrieb Chia-I Wu:
> > Userspace might poll a syncobj with the query ioctl. Call
> > dma_fence_enable_sw_signaling to ensure dma_fence_is_signaled returns
> > true in finite time.
>
> Wait a second, just querying the fence status is absolutely not
> guaranteed to return true in finite time. That is well documented on the
> dma_fence() object.
>
> When you want to poll on signaling from userspace you really need to
> call poll or the wait IOCTL with a zero timeout. That will also return
> immediately but should enable signaling while doing that.
>
> So just querying the status should absolutely *not* enable signaling.
> That's an intentional separation.
I think it depends on what semantics DRM_IOCTL_SYNCOBJ_QUERY should have.
If DRM_IOCTL_SYNCOBJ_QUERY is mainly for vulkan timeline semaphores,
it is a bit heavy if userspace has to do a
DRM_IOCTL_SYNCOBJ_TIMELINE_WAIT before a query.
>
> Regards,
> Christian.
>
> >
> > Fixes: 27b575a9aa2f ("drm/syncobj: add timeline payload query ioctl v6")
> > Signed-off-by: Chia-I Wu <olvaffe@xxxxxxxxx>
> >
> > ---
> >
> > v2: add Signed-off-by and Fixes tags
> > ---
> > drivers/gpu/drm/drm_syncobj.c | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
> > index 4fcfc0b9b386c..58c5593c897a2 100644
> > --- a/drivers/gpu/drm/drm_syncobj.c
> > +++ b/drivers/gpu/drm/drm_syncobj.c
> > @@ -1689,6 +1689,9 @@ int drm_syncobj_query_ioctl(struct drm_device *dev, void *data,
> > DRM_SYNCOBJ_QUERY_FLAGS_LAST_SUBMITTED) {
> > point = fence->seqno;
> > } else {
> > + /* ensure forward progress */
> > + dma_fence_enable_sw_signaling(fence);
> > +
> > dma_fence_chain_for_each(iter, fence) {
> > if (iter->context != fence->context) {
> > dma_fence_put(iter);
>
