linux-kernel - Re: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with sched_domain

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Date:	Mon, 16 May 2016 18:26:00 +0100
From:	Dietmar Eggemann <dietmar.eggemann@....com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...nel.org, linux-kernel@...r.kernel.org, clm@...com,
	matt@...eblueprint.co.uk, mgalbraith@...e.de, tglx@...utronix.de,
	fweisbec@...il.com
Subject: Re: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with
 sched_domain_shared

On 16/05/16 18:02, Peter Zijlstra wrote:
> On Mon, May 16, 2016 at 04:31:08PM +0100, Dietmar Eggemann wrote:
>> On 09/05/16 11:48, Peter Zijlstra wrote:
>>
>> Couldn't you just always access sd->shared via
>> sd = rcu_dereference(per_cpu(sd_llc, cpu)) for
>> updating nr_busy_cpus?
> 
> Sure; but why would I want to add that extra dereference? Note that in
> the next patch I add more users of sd_llc_shared.
> 

I see ... I thought because you do this already in
set_cpu_sd_state_[busy|idle]. But there you need the sd reference to set
sd->nohz_idle already.