Messages in this thread | | | Date | Thu, 8 Oct 2015 17:59:53 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH 3/3] stop_machine: change cpu_stop_queue_two_works() to rely on stopper->enabled |
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On 10/08, Peter Zijlstra wrote: > > On Thu, Oct 08, 2015 at 04:51:36PM +0200, Oleg Nesterov wrote: > > @@ -261,12 +276,8 @@ int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void * > > set_state(&msdata, MULTI_STOP_PREPARE); > > > > /* > > + * We do not want to migrate to inactive CPU. FIXME: move this > > + * into the caller. > > */ > > if (!cpu_active(cpu1) || !cpu_active(cpu2)) { > > preempt_enable(); > > So we cannot move that into the caller..
Why?
> because this function sleeps > with wait_for_completion(). > > Or rather, it would force the caller to use get_online_cpus(), which we > worked really hard to avoid.
Aaah wait. Sorry for confusion!
I meant "move this into the callback, migrate_swap_stop()".
> Also, I think we still want the patch I proposed which ensures the > stopper thread is active 'early', because the load balancer pretty much
Perhaps. Although I do not really understand why it is important. I mean, either way we unpark it at CPU_ONLINE stage, just sched_cpu_active() has a higher priority.
But this is off-topic in a sense that the main point of this patch is that stop_two_cpus() no longer needs to abuse cpu_active() checks to avoid the race with cpu_up/down, we can simply rely on ->enabled.
And again, we need to take both locks to remove "lglock stop_cpus_lock".
So I think your change can be applied after this series too. Or I missed something?
Oleg.
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