test step time of cpp, updateCheck / updateVariable / checkParity 3.0ms 0.4ms 0.6us
check parity in cpu , even faster a bit
ready to optimize kernel - updateVariableNode
nvprof kernel - updateVariable,
read add  write
x+1  x+1  x+1
result : instruction latency / execution dependency
add and write need to wait all data to be read, so read add write must execute serially,
solution: too few instructions to parallel, so can not optimize any longer