schedule exit too slow when PD leader changed

[bufferflies]

Bug Report

What did you do?

I find PD leader exit slow when I transfer leader

[2021/09/23 11:20:25.797 +08:00] [INFO] [leader.go:489] ["leader is deleted"]
[2021/09/23 11:20:25.800 +08:00] [ERROR] [client.go:172] ["region sync with leader meet error"] [error="[PD:grpc:ErrGRPCRecv]rpc error: code = Canceled desc = context canceled"]
[2021/09/23 11:20:26.800 +08:00] [INFO] [server.go:1099] ["leader changed, try to campaign leader"]
[2021/09/23 11:34:12.902 +08:00] [INFO] [coordinator.go:654] ["scheduler has been stopped"] [scheduler-name=balance-region-scheduler] [error="context canceled"]
[2021/09/23 11:34:12.902 +08:00] [INFO] [cluster.go:328] ["coordinator has been stopped"]

What did you expect to see?

I want that all scheduler exit cost less than 2min after leader changed.

What did you see instead?

What version of PD are you using (pd-server -V)?

master

[mayjiang0203]

/severity Major
/assign @bufferflies