On Wed, 20 May 2009, GeunSik Lim wrote: > 2009/5/20 GeunSik Lim <leemgs1@xxxxxxxxx>: > > > > > > Dear Ingo, > > > > > > I made 2 patch files again about static prioriy levels according to ingo's advice > > and explanation. (Reference: http://marc.info/?t=124211992800003&r=1&w=2 archives. ) > > > > Fix static priority related range and chart map(userspace/kernelspace) of ftrace. > > - about chart map of static priority in ftrace.txt file > > - about static priority levels(range) in sched-rt-group.txt file > > > > > > commit d6af702008117ca489a2f5476239d1688a517e98 > > Author: GeunSik,Lim <leemgs1@xxxxxxxxx> > > Date: Tue May 12 17:20:32 2009 +0900 > > > > sched: fix typo in sched-rt-group.txt file > > > > Fix typo about static priority's range. > > > > * Kernel Space priority 0(high) to 99(low) --> User Space RT priority 99(high) to 1(low) > > * Kernel Space priority 100(high) to 139(low)--> User Space nice -20(high) to 19(low) > > > > Ingo, > I want to change some descriptions according to below discussion. > > before) * Kernel Space priority 0(high) to 99(low) --> User Space RT > priority 99(high) to 1(low) > after) * Kernel Space priority 0(high) to 98(low) --> User Space > RT priority 99(high) to 1(low) > > I want to your advice and opinion about this changes. > > If I mistook, Please correct me. > > thks. > > > > Steven Rostedt: > Shouldn't that be: > Kernel priority: 0(high) to 98(low) ==> user RT priority 99(high) to 1(low) > > GeunSik Lim : > Thank you for your opinion. I think about corrected expression for > quick chart to map between kernel space and user space in ftrace . > > Steven Rostedt: > 100 items does not map to 99. Which begs the question, what can have > internal kernel priority 99? > > GeunSik Lim : > ok. Below example is about kernel (static) priority 99 that you said. > please, refer > to http://www.kernel.org/doc/man-pages/online/pages/man2/sched_setscheduler.2.html > webpage. > > For processes scheduled under one of the normal scheduling policies > (SCHED_OTHER, SCHED_IDLE, SCHED_BATCH), sched_priority is not used in > scheduling decisions (it must be specified as 0). > > int main (int argc, char **argv) > { int pidnumber, ret; > struct sched_param p; > p.sched_priority = 0; <------ Kernel (static) priority. > if (argc != 2) { > printf("usage: setbatch <pid>\n"); > exit(-1); > } > pidnumber = atol(argv[1]); > /* 3 = Number of SCHED_BATCH Constant */ > ret = sched_setscheduler(pidnumber, 3, &p); > if (ret) { > printf("could not set pid %d to SCHED_BATCH: err %d.\n", pid, ret); > return -1; > } > printf("pid %d is SCHED_BATCH from now on.\n", pid); > return 0; > } > > > > > > Processes scheduled with SCHED_OTHER or SCHED_BATCH must be assigned > > the static priority 0. Processes scheduled under SCHED_FIFO or SCHED_RR > > can have a static priority in the range 1 to 99. > > (reference: $> man 2 sched_setscheduler) > > > > Signed-off-by: GeunSik Lim <geunsik.lim@xxxxxxxxxxx> > > > > diff --git a/Documentation/scheduler/sched-rt-group.txt b/Documentation/scheduler/sched-rt-group.txt > > index 5ba4d3f..1537146 100644 > > --- a/Documentation/scheduler/sched-rt-group.txt > > +++ b/Documentation/scheduler/sched-rt-group.txt > > @@ -169,7 +169,7 @@ get their allocated time. > > > > Implementing SCHED_EDF might take a while to complete. Priority Inheritance is > > the biggest challenge as the current linux PI infrastructure is geared towards > > -the limited static priority levels 0-139. With deadline scheduling you need to > > +the limited static priority levels 0-99. With deadline scheduling you need to > > do deadline inheritance (since priority is inversely proportional to the > > deadline delta (deadline - now). Note, this document deals with internal kernel manipulations. The "prio" inside the kernel is indeed 0-139. Actually, if we count the idle task, it is 0-140. The PI code will also deal with non RT tasks so it is correct to say that the priority inheritance deals with 0-139 (I don't think the idle task ever touches anything needing PI). The sched_setscheduler user API uses a different priority mapping. I was looking at the code inside sched.c and I believe this is the mapping: 0 to 98 - maps to RT tasks 99 to 1 (SCHED_RR or SCHED_FIFO) 99 - maps to internal kernel threads that want to be lower than RT tasks but higher than SCHED_OTHER tasks. Although I'm not sure if any kernel thread actually uses this. I'm not even sure how this can be set, because the internal sched_setscheduler function does not allow for it. 100 to 139 - maps nice levels -20 to 19. These are not set via sched_setscheduler, but are set via the nice system call. 140 - reserved for idle tasks. -- Steve
