Added a file to compute the gpu transfer latency including theano overhead.

theano/misc/latence_gpu_transfert.py

+import time
+
+import numpy
+
+import theano
+
+y = theano.tensor.fvector()
+x = theano.shared(numpy.zeros(1,dtype='float32'))
+f1 = theano.function([y],updates={x:y})
+f2 = theano.function([],theano.sandbox.cuda.host_from_gpu(x))
+print f1.maker.env.toposort()
+print f2.maker.env.toposort()
+for i in [1,10,100,1000, 10000, 100000,1000000, 10000000]:
+    o = numpy.zeros(i, dtype='float32')
+    t0=time.time();f1(o);t1=time.time();
+    tf1=t1-t0
+    t0=time.time();f2();t1=time.time();
+
+    print  "%8i %6.1f ns %7.1f ns"%(i, tf1*1e6,(t1-t0)*1e6)