Re: [RFC] Restrict kernel spawning of threads to a specified set of cpus.

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Thu, Sep 12, 2013 at 08:35:05PM +0200, Frederic Weisbecker wrote:
> On Thu, Sep 12, 2013 at 08:39:22AM -0700, Paul E. McKenney wrote:
> > On Thu, Sep 12, 2013 at 05:11:04PM +0200, Frederic Weisbecker wrote:
> > > 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.
> > 
> > OK, I will bite...  How do you handle the case where you have collected
> > all the kthreads, one of the kthreads spawns another kthread, then you
> > set affinity on the collected kthreads, which does not include the newly
> > spawned one?
> 
> Just offline the CPUs you want to isolate, affine your kthreads and re-online
> the CPUs.
> 
> If you're lucky enough to have 1024 CPUs, a winter night should be enough ;-)

Running at RT prio 99 to reduce the probability of respawns?  ;-)

							Thanx, Paul