Messages in this thread | | | Date | Thu, 12 Sep 2013 17:11:04 +0200 | From | Frederic Weisbecker <> | Subject | Re: [RFC] Restrict kernel spawning of threads to a specified set of cpus. |
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On Thu, Sep 12, 2013 at 02:52:56PM +0000, Christoph Lameter wrote: > On Thu, 12 Sep 2013, Frederic Weisbecker wrote: > > > > > Ok but you can change the affinity of a kthread from userspace, as > > > > long as you define a cpu set that is among that kthread's cpus allowed. > > > > > > Ok but at that point kthread has already spawned a lot of kernel threads. > > > > > > The same is true for init and kmod. > > > > > > > Ok but then we just need to set the affinity of all these kthreads. > > A simple lookup on /proc/[0-9]+/ should do the trick. > > Yea but the kernel option makes it easy. No extras needed. Kernel brings > it up user space cleanly configured and ready to go.
Ok but really that's just two lines of bash. I really wish we don't complicate core kernel code for that.
I think we all agree that the big issue here is that CPU isolation requires to set up a fragmented set of features and it's not at all obvious to do it correctly: full dynticks, rcu nocbs, kthreads affinity, timer_list, hrtimers, workqueues, IPIs, etc...
So IMHO what is missing is a reliable userspace tool that can handle all that: do the checks on pre-requirements, handle the kthreads and even user task affinity, tweak some sysctl stuffs to turn off features that generate noise, etc...
> This also allows us to cleanup kernel uses of cpumasks in such a way that > proper thread placement for various other uses (reclaim f.e. kswpad) is > possible.
Same here, a central tool should be able to solve that.
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