Messages in this thread | | | Subject | Re: RT-Scheduler/cgroups: Possible overuse of resources assigned via cpu.rt_period_us and cpu.rt_runtime_us | From | Peter Zijlstra <> | Date | Wed, 18 Jun 2008 16:37:16 +0200 |
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On Wed, 2008-06-18 at 16:12 +0200, Daniel K. wrote: > mkdir /dev/cgroup > mount -t cgroup -o cpu,cpuset cgroup /dev/cgroup > > mkdir /dev/cgroup/0 > > echo 3 > /dev/cgroup/0/cpuset.cpus > echo 0 > /dev/cgroup/0/cpuset.mems > echo 100000 > /dev/cgroup/0/cpu.rt_period_us > echo 5000 > /dev/cgroup/0/cpu.rt_runtime_us > > schedtool -R -p 1 -e burnP6 & > [1] 3309 > echo 3309 > /dev/cgroup/0/tasks > > At this point I'd expect the burnP6 task to use 5% of the available CPU > resources in the cgroup (5000/100000), but the real CPU usage, as > reported by top, is 20% This is 4 times the expected result, and as I > have 4 cores, I think there is a strong hint of correlation there. > > Maybe with a 4 core system there really is 4 000 000 us available for > every 1 wall-time second?
Indeed. In effect each cpu (see below on specifics) gets the runtime/period you specify, and it moves unused runtime between cpus.
> However, I have only assigned one core (3) to _this_ cgroup, so I think > this cgroup is overusing its assigned resources. > > What do you think?
I think you're on to something :-)
It uses root domains, that is the largest domain this cpu is part of that has load-balancing enabled.
So while you have made your process part of the cgroup and the cpuset, there is no strong relation between them, that is to say, I could either mount the cpuset or cpu controller on a different mount point and add tasks to one but not the other.
So the relation I used is that of load-balance domains.
So in order to get what you intended, do something like:
mount none /dev/cpuset cgroup -o cpuset mount none /cgroup/cpu cgroup -o cpu
mkdir /dev/cpuset/root mkdir /dev/cpuset/rt
# # this might not actually make the kernel happy # as it might attempt (and possibly succeed in) # moving cpu bound kernel threads # for i in `cat /dev/cpuset/tasks`; do echo $i > /dev/cpuset/root/tasks; done
echo 0-2 > /dev/cpuset/root/cpuset.cpus echo 3 > /dev/cpuset/rt/cpuset.cpus
echo 0 > /dev/cpuset/cpuset.sched_load_balance
mkdir /cgroup/cpu/foo echo 100000 > /cgroup/cpu/foo/cpu.rt_period_us echo 5000 > /cgroup/cpu/foo/cpu.rt_runtime_us
echo $$ > /dev/cpuset/rt/tasks echo $$ > /cgroup/cpu/foo/tasks
chrt -r -p 1 burnP6 &
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