In old drivers there was a bug in getting the current GPU time on Vega GPUs, as described also here:
glGetInteger64v(GL_TIMESTAMP, ...) broken on Vega
This was fixed in later drivers, but the behavior is still not correct. Using the following code fragment:
//create a query objectGLuint qry;glGenQueries(1, &qry);//get current GPU time on the CPU, synchronous callGLint64 vcpu;glGetInteger64v(GL_TIMESTAMP, &vcpu);//push a timestamp queryglQueryCounter(qry, GL_TIMESTAMP);//fetch the timestamp value immediately//normally this would be done only later after a fence, but the bug shows this way tooGLuint64 v;glGetQueryObjectui64v(qry, GL_QUERY_RESULT, &v);//this fails on Vega, (19.10.1 checked)assert(v >= vcpu);
Note this technique is used to measure pipeline latency and is described also in OpenGL Superbible by Graham Sellers.
The time returned by the glGetInteger64v(GL_TIMESTAMP, ...) call should be lower than the time when the later query has been executed.
