improve dashboard loading speed

[shizunge]

We may use Prometheus increase fuction to speed up loading the clients.

But there are clients missing due to how Grafana samples the data.

The increase function generate a pulse whose width is half of the sample period.
e.g.
if Ganfana samples at time -4, -2, 0, 2, 4
Then the the pulse generated by increase will be last from 0-1, or 1-2. The pulse at 1-2 will not be captured by Grafana.