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Guillaume Lemaître
Guillaume Lemaître

Reputation: 1280

Thread scheduling priority and niceness

Under GNU/Linux, niceness represents thread scheduling priority. Lowest niceness corresponds to highest priority.

Considering only scheduler based on priorities (no time slicing), is anyone aware of a wide-spread OS implementation where the behaviour would be different, i.e. highest niceness corresponds to highest priority?

Upvotes: 0

Views: 899

Answers (1)

user2958595
user2958595

Reputation: 36

One of the problems with "priority" is that its semantics are overloaded in practice. Formally, it is a mechanism with the minimal semantics that it induces an uninterpreted partial ordering. So scheduling eligibility can be denoted by larger to smaller priority integers interpreted as more to less eligible, or in the opposite order. But different systems and users employ the priority mechanism with several different additional richer semantics. In some cases, priority is interpreted as urgency. In some other cases it is interpreted as relative importance. It is even occasionally used for establishing precedence. Your question implies associating priority with the semantics of GNU/Linux "niceness." You asked if anyone knows of a wide-spread OS that has the reverse semantics. As the other replies noted, that would make priority have the semantics of "un-niceness." Strictly speaking, that is not the same as making the niceness-based priorities work "backwards." So your question is ill-formed. I am unaware of any OS that has niceness semantics and assigns priorities in un-nice order. You might have been thinking of whether there are wide-spread OS's in which scheduling eligibility is inversely related to priority integers--the answer to that is "yes." But note that too is not a well-formed question: by definition (admittedly not widely understood) scheduling eligibility is the same as uninterpreted priority per se, unless additional semantics are added to "priority." For example, if priority is specified as an 8-bit integer, the semantics of scheduling eligibility can be that larger priorities correspond to greater eligibility, or that smaller ones correspond to greater eligibility--each option has been chosen by various OS's.

Upvotes: 2

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