Re: [PATCH v5] nohz: set isolcpus when nohz_full is set

[Mike Galbraith <umgwanakikbuti@gmail.com>]

On Thu, 2015-04-09 at 19:12 +0200, Peter Zijlstra wrote:
> On Thu, Apr 09, 2015 at 12:59:39PM -0400, Chris Metcalf wrote:
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index 6d77432e14ff..18a961b9beba 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -323,6 +323,7 @@ struct task_struct;
> >  extern int lockdep_tasklist_lock_is_held(void);
> >  #endif /* #ifdef CONFIG_PROVE_RCU */
> >  
> > +extern void sched_isolated_map_add(const struct cpumask *);
> >  extern void sched_init(void);
> >  extern void sched_init_smp(void);
> >  extern asmlinkage void schedule_tail(struct task_struct *prev);
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index f0f831e8a345..b055c5e0e65c 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -5824,6 +5824,11 @@ static int __init isolated_cpu_setup(char 
> > *str)
> >  
> >  __setup("isolcpus=", isolated_cpu_setup);
> >  
> > +void sched_isolated_map_add(const struct cpumask *cpumask)
> > +{
> > +   cpumask_or(cpu_isolated_map, cpu_isolated_map, cpumask);
> > +}
> > +
> >  struct s_data {
> >     struct sched_domain ** __percpu sd;
> >     struct root_domain      *rd;
> > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> > index a4c4edac4528..b0092d02ca3f 100644
> > --- a/kernel/time/tick-sched.c
> > +++ b/kernel/time/tick-sched.c
> > @@ -385,6 +385,9 @@ void __init tick_nohz_init(void)
> >     for_each_cpu(cpu, tick_nohz_full_mask)
> >             context_tracking_cpu_set(cpu);
> >  
> > +   /* It's not meaningful to be nohz without disabling the 
> > scheduler. */
> > +   sched_isolated_map_add(tick_nohz_full_mask);
> > +
> >     cpu_notifier(tick_nohz_cpu_down_callback, 0);
> >     pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n",
> >             cpumask_pr_args(tick_nohz_full_mask));
> 
> Right, this could work. Although I would suggest adding a comment
> somewhere that we should be careful with init order. I checked, this
> appears to be ordered right, but...

I'd embed it in domain construction, that way it'd be ready for the 
day nohz_full becomes dynamic, and people can start using cpusets to 
set up /tear down isolated sets on the fly.

        -Mike