Messages in this thread | | | Date | Thu, 12 Oct 2017 14:57:29 -0700 (PDT) | From | David Rientjes <> | Subject | Re: [RFC 1/2] cgroup, kthread: do not allow moving kthreads out of the root cgroup |
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On Thu, 12 Oct 2017, Peter Zijlstra wrote:
> > Attaching kernel threads to a non-root cgroup is generally a bad > > idea. Kernel threads are generally performing the work required > > to keep the system working and healthy, and applying various > > resource limits may affect system stability and performance. > > > > Some examples of dangerous behavior are limiting CPU time available > > to rcu stuff, memory limits applied to almost all kthreads, etc. > > > > To prevent this dangerous behavior, let's deny all kthread > > movements between cgroups. Right now only kthreads bounded > > to CPUs are not allowed to move, which is not sufficient. > > > > If there are examples of kthreads which can be limited, > > and it's guaranteed to be safe, we can allow explicit > > exceptions further. > > The traditional use-case is stuffing all the unbound kthreads into a > system cpuset in order to limit 'crap' on the rest of the CPUs. > This setup is typically found in HPC and RT environments. > > So NAK. This needs to stay working in as far as it still works. >
+1, I originally introduced PF_THREAD_BOUND to cpusets in 2008 to prevent migration threads and software watchdog threads from being able to access the cpus they work on. We also move unbound kthreads to a system cpuset.
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