linux-kernel - Re: [PATCH v4] sched: fix init NOHZ

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Date:	Tue, 26 Feb 2013 14:16:38 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	linux-kernel@...r.kernel.org, linaro-dev@...ts.linaro.org,
	peterz@...radead.org, mingo@...nel.org, rostedt@...dmis.org,
	efault@....de
Subject: Re: [PATCH v4] sched: fix init NOHZ_IDLE flag

2013/2/22 Vincent Guittot <vincent.guittot@...aro.org>:
> 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.
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