2011/9/26 Mulyadi Santosa <mulyadi.santosa@xxxxxxxxx>: > Hi :) > >>Actually, the CFS scheduler which >> is a new scheduler in Linux kernel also does the same thing. But, I >> think this way does not fit with scheduler's principle. > > remember the keyword you ask? "fairness"? that is being fair to all > processes.... but since, there are always more processes than > processors, unfairness always happen..... > In fact, I am interested in the length of timeslice rather than fairness at this point. :-) >>This way ensures >> lower latency. It is also necessary that CPU-bound processes are to be >> allocated longer timeslice to improve throughput owing to less process >> switch costs. That means lower priority processes (CPU-bound) should >> be allocated longer timeslice, whichs obviously conflicts with the >> actual practice taken by the Linux's scheduler. Any explanation? > > What you refer initially is the time when time slice assignment is > strictly derived from the static/nice level. So e.g process with nice > level 0 has lesser time slice that nice level -5. > > But as you can see, situation change dynamically during run time, thus > static prio must be taken into dynamic priority. And dynamic priority > itself, must take another factor for time slice calculation. Here, > sleep time comes into play. > Ok, suppose that there is a CPU-bound process and a I/O-bound process, both of them are allocated the same nice level 0. After some time, the I/O-bound process will receive higher dynamic priority owing to its frequent sleeping. Now that the I/O-bound process more like to sleep, why does the scheduler give it longer timeslice? After all, it really does not need more time. On ther other hand, the CPU-bound process will receive lower dynamic priority as its punishment because it costs more CPU time. Lower dynamic priority indicates this process is more 'CPU-bound', that is this process need more CPU time. If the scheduler allocates longer timeslice for this process, the frequency of process switch will be reduced. I think that will help to improve throughput of the entire system. _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
