Re: [PATCH v4] sched: fix init NOHZ_IDLE flag

[Vincent Guittot]

On 26 February 2013 14:16, Frederic Weisbecker <fweisbec@xxxxxxxxx> wrote:
> 2013/2/22 Vincent Guittot <vincent.guittot@xxxxxxxxxx>:
>> I wanted to avoid having to use the sd pointer for testing NOHZ_IDLE
>> flag because it occurs each time we go into idle but it seems to be
>> not easily feasible.
>> Another solution could be to add a synchronization step between
>> rcu_assign_pointer(dom 1, NULL) and create new domain to ensure that
>> all pending access to old sd values, has finished but this will imply
>> a potential delay in the rebuild  of sched_domain and i'm not sure
>> that it's acceptable
>
> The other issue is that we'll need to abuse the fact that struct
> sched_domain is per cpu in order to store a per cpu state there.
> That's a bit ugly but at least safer.
>
> Also, are struct sched_group and struct sched_group_power shared among
> several CPUs or are they per CPUs allocated as well? I guess they
> aren't otherwise nr_cpus_busy would be pointless.

Yes they are shared between CPUs, per cpu sched_domain points to same
sched_group and sched_group_power.
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