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15

It's for what I'd call policy reasons. The idea is that normal users can't override the actions of privileged users. Let's say you're a user on some enormous shared server. You're running monstrous CPU-hogging processes to the detriment of the other users. The sysadmin renices some of your processes because he doesn't like you very much. The OS doesn't ...


14

Since linux 2.6.12, that depends on the value of the RLIMIT_NICE limit (ulimit -e). Which can take values from 0 to 40. That limit is more the limit on the priority of the process (the greater that number, the higher the priority a user can set for a process). You'll notice the default value is 20 on ubuntu 10.04 and 0 in Debian jessie for instance. A ...


11

What does a niceness of (-) indicate? Notice those also have a PRI score of -100; this indicates the process is scheduled as a realtime process. Realtime processes do not use nice scores and always have a higher priority than normal ones, but still differ with respect to one another. You can view details per process with the chrt command (e.g. chrt -p ...


5

renice does affect the priority of a process. But as you've experienced, just because a process has higher priority doesn't imply that it will have all the resources it needs. A higher priority merely gives the process a bigger chance to grab resources. renice only affects CPU time. So it only has an effect if two or more processes are competing for CPU ...


4

@Goldlilock's answer directed me to do the research in the right path. This is my research details. Scheduling Algorithms available for processes Linux supports 3 scheduling policies. SCHED_FIFO, SCHED_RR, and SCHED_OTHER. SCHED_OTHER is the default universal time-sharing scheduler policy used by most processes; SCHED_FIFO and SCHED_RR are intended for ...


3

I am wondering why top and htop don't display -100 for higest priority real time processes ? That's because SCHED_RR and SCHED_FIFO have fixed static priorities from 1-99: Source For realtime priorities, the order is reversed: 99 is indeed the highest one, contrary to the ususal "lower is higher". Per your comment I misunderstood your question, ...


2

In fact, RLIMIT_NICE allows you to bypass the basic rule that says that "a process can raise its nice value only if owned by root". Demonstration: # ulimit -e 30 # su nobody $ nice -n -10 top You will see that your top process runs with niceness -10. Now if you try nice -n -11 top, it will run with niceness 0, because -11 is not allowed by ...


2

Under Linux, by default, a process's IO priority is derived from its CPU priority according to the formula io_priority = (cpu_nice + 20) / 5 IO priority ranges from 0 to 7 with 0 being the highest priority. CPU niceness ranges from -20 to 19 with -20 being the highest priority. You can use the ionice command to change a process's IO priority. If you want ...


1

In order to make your CPU use less battery, you need it to run slower. The total amount of CPU instructions needed to execute your program do not depend on the speed at which it runs, so limiting the proportion of CPU time used by your program would make it use more CPU, not less. When your CPU is doing nothing instead of running your program, it's still ...


1

Process priority is not the only thing that comes into play when you are trying to tweak user experience. Compiling the kernel is a rather I/O-heavy thing - lots of reading/writing from/to small files which can stretch the file system quite a bit (there is a reason why it is sometimes used as a benchmark in its own right), especially on a multiprocessor ...



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