Normal processing time is 180 days as per law. Congress passed the bill and President signed that bill. So USCIS has to abide that law. Also USCIS has to submit backlog reduction reports to congress in timely manner. But I don't think they are submitting any report to congress and also they didn't reduce the backlog. Since USCIS didn't abide by that law, it is time to approach the judicial branch to take proper action against USCIS.
According to the Immigration Service and Infrastruture Improvement Act of 2000, SEC. 203,
(1) Backlog.--The term ``backlog'' means, with respect to an immigration benefit application, the period of time in excess of 180 days that such application has been pending before the Immigration and Naturalization Service.
Also, according to SEC.202. PURPOSES (b) POLICY,
It is the sense of Congress that the processing of an immigration benefit application should be completed not later than 180 days after the initial filing of the application.