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SubjectRe: [PATCH tip/core/rcu 07/23] rcu: Provide OOM handler to motivate lazy RCU callbacks
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On Thu, 2012-09-06 at 10:41 -0700, Paul E. McKenney wrote:
> On Thu, Sep 06, 2012 at 09:52:53AM -0400, Steven Rostedt wrote:
> > On Thu, 2012-09-06 at 15:46 +0200, Peter Zijlstra wrote:
> > > On Thu, 2012-08-30 at 11:18 -0700, Paul E. McKenney wrote:
> > > > + get_online_cpus();
> > > > + for_each_online_cpu(cpu)
> > > > + for_each_rcu_flavor(rsp)
> > > > + smp_call_function_single(cpu, rcu_oom_notify_cpu,
> > > > + rsp, 1);
> > > > + put_online_cpus();
> > >
> > > I guess blasting IPIs around is better than OOM but still.. do you
> > > really need to wait for each cpu individually, or would a construct
> > > using on_each_cpu() be possible, or better yet, on_each_cpu_cond()?
>
> I rejected on_each_cpu_cond() because it disables preemption across
> a scan of all CPUs. Probably need to fix that at some point...

It would be rather straight fwd to make a variant that does
get_online_cpus() though.. but even then there's smp_call_function()
that does a broadcast, avoiding the need to spray individual IPIs and
wait for each CPU individually.


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