Merge pull request #433 from JuliaGPU/tb/time_sync

Synchronize the GPU while doing time measurements.

Author: maleadt

src/memory.jl

@@ -202,13 +202,30 @@ macro allocated(ex)
     end
 end
 
+
+"""
+    @time ex
+
+Run expression `ex` and report on execution time and GPU/CPU memory behavior. The GPU is
+synchronized right before and after executing `ex` to exclude any external effects.
+
+"""
 macro time(ex)
     quote
+        # @time might surround an application, so be sure to initialize CUDA before that
+        # FIXME: this should be done in CUDAdrv (`synchronize(ctx=CuCurrentOrNewContext()`)
+        #        but the CUDA initialization mechanics are part of CUDAnative.jl
+        CUDAnative.maybe_initialize("@time")
+
+        # coarse synchronization to exclude effects from previously-executed code
+        CUDAdrv.synchronize()
+
         local gpu_mem_stats0 = copy(alloc_stats)
         local cpu_mem_stats0 = Base.gc_num()
         local cpu_time0 = time_ns()
 
-        local val = $(esc(ex))
+        # fine-grained synchronization of the code under analysis
+        local val = @sync $(esc(ex))
 
         local cpu_time1 = time_ns()
         local cpu_mem_stats1 = Base.gc_num()