eap authentication and cpu utilization

[Alan DeKok]

Norbert Wegener wrote:
> Do you also have experience in how many percent of that theoretic value
> can be reached in practise with a database backend on the same machine
> where beside freeradius and the database nothing else is running?

  I don't have hard numbers, unfortunately.  It also depends on the
number, and kind of queries the server does for each request.

  If you do a simplistic analysis, you could assume that the two
processes are simply stealing CPU time from each other.  If I recall my
numerical analysis courses...

  E = # of EAP requests/s (say 30 on a normal machine)
  Q = # of SQL qeuries/s  (likely 1000 un-cached on a normal machine)

  Assuming one SQL query per EAP transaction, we have 'E' SQL queries/s.
 So E/Q = 3% of CPU time is being used for SQL.  That is stolen directly
from EAP requests, so there is 97% CPU time left, or .97*30 = 29 EAP
transactions/s as a theoretical maximum.

  Realistically, there is a lot more overhead than this.  But I would be
surprised if it lowered the maximum number of EAP sessions by more than
10-20%.

  Alan DeKok.