On Friday 23 August 2002 05:09 am, Wank Rainer wrote: > Hi, > > the Linux scheduler has three policies SCHED_FIFO, SCHED_RR and > SCHED_OTHER. SCHED_FIFO and SCHED_RR are for realtime requirements. > The kernel is not preemptive. That means that a process running in kernel > mode can not be preempted. > > There are also kernel threads, like [kswapd]. Does a kernel thread have a > priority? How does the scheduler schedule kernel threads? All processes on the system are scheduled exactly the same way. This means that a process with a priority higher than a kernel daemon will have precedence over the daemon. I've tried this. I ran a fifo thread the monopolized the CPU. I tried to connect a USB device but the khubd could not run. There are some daemons that have a real-time priority however, like certain sound daemons: artsd. Under the O(1) scheduler, there has been a little change that would allow certain kernel-created threads the obtain priorities that are not available to any other threads. However, last time I checked, this has not been put to use, but the mechanism is there. Secondly, a thread can be preempted in kernel mode from kernel 2.5.x and onward, but only in certain areas of the kernel where preemption is not enabled. > > On the other hand a process can also have several threads. > How does the scheduler schedule these threads in contrast to kernel threads > or processes? > > Thanx! > > Rainer -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
