linux-kernel - Re: [tip:sched/core] sched/cpuacct: Split usage accounting into user_usage and sys

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Message-ID: <20160406075000.GF3430@twins.programming.kicks-ass.net>
Date:	Wed, 6 Apr 2016 09:50:00 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Zhao Lei <zhaolei@...fujitsu.com>
Cc:	'Ingo Molnar' <mingo@...nel.org>,
	'Srikar Dronamraju' <srikar@...ux.vnet.ibm.com>,
	tglx@...utronix.de, efault@....de, htejun@...il.com,
	linux-kernel@...r.kernel.org, tj@...nel.org,
	torvalds@...ux-foundation.org, yangds.fnst@...fujitsu.com,
	hpa@...or.com
Subject: Re: [tip:sched/core] sched/cpuacct: Split usage accounting into
 user_usage and sys_usage

On Wed, Apr 06, 2016 at 03:47:18PM +0800, Zhao Lei wrote:
> > If you change the above loop to something like:
> > 
> > 	for (ca = task_ca(tsk); ca; ca = parent_ca(ca)) {
> > 		if (WARN_ON_ONCE(!ca->cpuusage))
> > 			continue;
> > 		this_cpu_ptr(ca->cpuusage)->usages[index] += cputime;
> 
> Or s/ this_cpu_ptr/get_cpu_var to avoid preempt?

This is all called with rq->lock held, preemption is firmly disabled.