On 11/07/17 06:09 AM, Jason Ekstrand wrote: > On Mon, Jul 10, 2017 at 9:15 AM, Christian König > <deathsimple at vodafone.de <mailto:deathsimple at vodafone.de>> wrote: > > Am 10.07.2017 um 17:52 schrieb Jason Ekstrand: >> On Mon, Jul 10, 2017 at 8:45 AM, Christian König >> <deathsimple at vodafone.de <mailto:deathsimple at vodafone.de>> wrote: >> >> Am 10.07.2017 um 17:28 schrieb Jason Ekstrand: >>> On Wed, Jul 5, 2017 at 6:04 PM, Dave Airlie >>> <airlied at gmail.com <mailto:airlied at gmail.com>> wrote: >>> [SNIP] >>> So, reading some CTS tests again, and I think we have a >>> problem here. The Vulkan spec allows you to wait on a fence >>> that is in the unsignaled state. >> >> At least on the closed source driver that would be illegal as >> far as I know. >> >> >> Then they are doing workarounds in userspace. There are >> definitely CTS tests for this: >> >> https://github.com/KhronosGroup/VK-GL-CTS/blob/master/external/vulkancts/modules/vulkan/synchronization/vktSynchronizationBasicFenceTests.cpp#L74 >> <https://github.com/KhronosGroup/VK-GL-CTS/blob/master/external/vulkancts/modules/vulkan/synchronization/vktSynchronizationBasicFenceTests.cpp#L74> >> >> >> You can't wait on a semaphore before the signal operation is >> send down to the kerel. >> >> >> We (Intel) deal with this today by tracking whether or not the >> fence has been submitted and using a condition variable in >> userspace to sort it all out. > > Which sounds exactly like what AMD is doing in it's drivers as well. > > > Which doesn't work cross-process so... Surely it can be made to work by providing suitable kernel APIs to userspace? >> If we ever want to share fences across processes (which we do), >> then this needs to be sorted in the kernel. > > That would clearly get a NAK from my side, even Microsoft forbids > wait before signal because you can easily end up in deadlock situations. > > Please don't NAK things that are required by the API specification and > CTS tests. There is no requirement for every aspect of the Vulkan API specification to be mirrored 1:1 in the kernel <-> userspace API. We have to work out what makes sense at each level. > That makes it very hard for people like me to get their jobs done. :-) Jason, that's uncalled for. Christian is also just doing his job here. -- Earthling Michel Dänzer | http://www.amd.com Libre software enthusiast | Mesa and X developer
