When we restaet SQL Serveice, Very High CPU usage on SQL server

After a server (hardware) restart, or a SQL-Service restart, the usage is 80% to 90%
and i also restart my site and application pool service then restart my sql service
What is the reason of High CPU usage when we restart site, application pool and sql services.

do you use some sort of caching? membase, couchbase or anything like that

When SQL starts, it has to bring every database to a consistent state first. That takes some overhead. It's a lot more if one or more databases were not cleanly shut down when SQL service last stopped, because then SQL has to read the log file and re-apply or rollback db changes.