Am 22.09.2016 um 13:16 schrieb Gustavo Padovan: > 2016-09-22 Christian König <christian.koenig at amd.com>: > >> Dropping the rest of the patch, cause that really doesn't make sense any >> more. >> >> Am 22.09.2016 um 12:40 schrieb Gustavo Padovan: >>>> E.g. for example it is illegal to do something like >>>>> "while(!fence_is_signaled(f)) sleep();" without enabling signaling before >>>>> doing this. >>>>> >>>>> Could just be a misunderstanding, but the comments on your patch actually >>>>> sounds a bit like somebody is trying to do exactly that. >>> I think the usecase in mind here is poll(fd, timeout=0) >> Exactly as I feared. Even if userspace polls with timeout=0 you still need >> to call enable_signaling(). >> >> Otherwise you can run into a situation where userspace only uses timeout=0 >> and so never activates the signaling check in the driver. >> >> This would in turn result in an endless loop on implementations where the >> driver never signals fences on their own. > Polling is optional, userspace may never call it. And DRM/KMS or GPU > drivers will be doing fence_wait() themselves so signaling is enabled at > some point.
No they won't. We have an use case where we clearly want to avoid that as much as possible because and so the driver never calls enable_signaling() on it's own. Exposing this poll function to userspace without enabling signaling is a clear NAK from my side. Christian. > > Gustavo >
