Thanks @cgrant and @mhagain for your kindly reply.
I knew it might make little sense to measure a shader in this naive way and it was difficult to isolate different stages. But since the actual temporal performances are closely guarded secrets of the chip vendors, that is the only way I can come up with. I took up this idea from ''In-Depth Performance Analyses of DirectX 9 Shading Hardware." from ShaderX3.
I knew this kind of measurement is old-fashioned, but is there some better ideas to give a coarse value to the artists that how fine is the geometry and how fine is the geometry and how much is the max chararacters a mobile device can support? There are several 3-rd party measurement tools like GPU ShaderAnalyze from AMD or ShaderPerf2 from NV. But they are not friendly to mobile Gpus.