Dashboard cannot use under heavy load

[breezewish]

Bug Report

Please answer these questions before submitting your issue. Thanks!

What did you do?

When TiDB is under heavy load, for example, needs more than 1 second to establish a connection, the TiDB dashboard cannot use any more, and we can no longer troubleshoot..

What did you expect to see?

Use TiDB Dashboard to diagnose problems.

What did you see instead?

TiDB Dashboard cannot sign in.

What version of TiDB Dashboard are you using (./tidb-dashboard --version)?

master