Hi Christian, On Sun, 23 May 2021 at 18:16, Christian König <christian.koenig@xxxxxxx> wrote: > Am 22.05.21 um 22:05 schrieb Daniel Stone: > > Anyway, the problem with syncobj is that the ioctl to wait for a > > sync_file to materialise for a given timeline point only allows us to > > block with a timeout; this is a non-starter, because we need something > > which fits into epoll. The most optimal case is returning a new > > eventfd or similar which signals when a given timeline point becomes > > available or signaled, but in extremis a syncobj FD becoming readable > > when any activity which would change the result of any zero-timeout > > wait on that syncobj is more or less workable. > > I think the tricky part is to epoll for a certain value. > > Not sure how eventfd is supposed to work, but IIRC we don't have the > functionality to poll for a certain value/offset etc to become available. > > We could of course create a separate fd for each requested value to poll > for thought, but that sounds like a bit much overhead to me. Yeah, I understand the point; something like an eventfd is exactly what you think, that we would have to materialise a new FD for it. On the other hand, as soon as the sync point becomes available, the winsys will want to immediately extract a sync_file from it, so I don't think FD amplification is a big issue. If it looks like being a problem in practice, we could look at providing a FD which starts off inert, and only later becomes a sync_file after it polls readable, but that sounds like something we really want to avoid if we can. Cheers, Daniel
