On Sat, Aug 28, 2010 at 06:35:03PM +0200, Michael Blizek wrote: > Hi! > > On 02:01 Sat 28 Aug , Pablo Antonio wrote: > ... > > I want to know if it's possible to create a real-time process with > > SCHED_FIFO policy that starts running and never lets any other process > > run again. > > Yes, it should be. However hardware interrupts will still arrive. I don't care about that. All I want is *no other processes* to run ever again, but kernel code in my process' context is alright. > > > I had read that processes in SCHED_FIFO usually run until a) they block > > themselves by calling some syscall (for example, an I/O request), b) > > they are preempted by some higher priority process or c) they decide to > > yield the processor. So I thought that technically it would be possible > > to create a process that "takes over" the processor from all the other > > processes: Just create a SCHED_FIFO process that loops infinitely. > > > > However, when I tried this it didn't work. Someone told me about > > sched_rt_runtime_us and sched_rt_period_us, which acted like a > > protection for this cases. So I tried both setting sched_rt_runtime_us > > to -1 and setting both values to the same number, but it didn't work > > either: I can switch to another terminal, execute top and see the > > process running. > > This is weird. Are you sure that you have put the process in the SCHED_FIFO > queue and assigned a static priority > 0 via sched_setscheduler? If you start > top and look in the PR column you should see "RT". Here's something I've been using. The first command sets the runtime value to the period value, so real-time process don't leave space for other processes to run. The others create process with SCHED_FIFO policy. $ cat /proc/sys/kernel/sched_rt_period_us | sudo tee /proc/sys/kernel/sched_rt_runtime_us $ time sudo chrt -f 99 bash -c 'seq 10000000 > /dev/null' In a two-core CPU I used: $ time sudo chrt -f 99 bash -c 'seq 10000000 > /dev/null' & time sudo chrt -f 99 bash -c 'seq 10000000 > /dev/null' For some reason, for priority numbers under 99 the PR column doesn't say RT. For example, for priority 98 it says -99. Those commands sometimes kind of hang the other processes but sometimes they don't. > > > What am I doing wrong? Is there some option in the kernel I have to > > enable/disable? > > I do not think that there is an option about this. :/ Thanks, -- Pablo Antonio (AKA crazy2k) http://www.pablo-a.com.ar/ -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
