An effective manager does two things first and foremost:

1) Make sure that his/her employees' day-to-day work aligns with the goals of the company

2) Remove any and all roadblocks keeping employees from being efficient and effective in their work, even if it means risking political capital.

I've always fantasized that if I ran a company, when annual reviews came around, the reviews would be bi-directional. In order words, employees must (confidentially) review their managers as well as vice-versa.

Someone will eventually respond, "okay, but if you let, say, engineers have that much control over how a company operates, you're not going to have a profitable company for very long." To which I would respond: that's why you set the company culture and also you have to be diligent about letting people go who are not a good fit for the company's goals.

Having working in management for years, both middle and upper, internal and external, as founder and in other companies: I have quite a strong stance against "confidentially".

Because the reality is that 80% of the typical workforce (maybe even more in the case of engineers) has a lot of comments about how things could be better and how their manager is doing it all wrong. And those comments tend to come out in an unnecessarily strong negative form if you provide an anonymous forum. But most companies don't need more people telling you what's wrong, they need people that take a responsibility in improving it and move things forward.

Are reviews of managers by employees that uncommon? At Google every manager is reviewed by a survey of their direct reports every performance cycle and that certainly feeds into assessment of manager performance.

I can't talk about the company as a whole, but in my circle at Arm reviews come from all the people who work with the reviewed. I did a review of my manager, requested by his manager.