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

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Date:	Wed, 6 Apr 2016 19:43:53 +0800
From:	Zhao Lei <zhaolei@...fujitsu.com>
To:	'Peter Zijlstra' <peterz@...radead.org>,
	'Anton Blanchard' <anton@...ba.org>
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>, 'Stephen Rothwell' <sfr@...b.auug.org.au>,
	'Michael Ellerman' <mpe@...erman.id.au>
Subject: RE: [tip:sched/core] sched/cpuacct: Split usage accounting into user_usage and sys_usage

Hi, Anton and Peter

> -----Original Message-----
> From: Peter Zijlstra [mailto:peterz@...radead.org]
> Sent: Wednesday, April 06, 2016 7:08 PM
> To: Anton Blanchard <anton@...ba.org>
> 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; zhaolei@...fujitsu.com;
> yangds.fnst@...fujitsu.com; hpa@...or.com; Stephen Rothwell
> <sfr@...b.auug.org.au>; Michael Ellerman <mpe@...erman.id.au>
> Subject: Re: [tip:sched/core] sched/cpuacct: Split usage accounting into
> user_usage and sys_usage
> 
> On Wed, Apr 06, 2016 at 08:32:19PM +1000, Anton Blanchard wrote:
> > Hi,
> >
> > > > >  void cpuacct_charge(struct task_struct *tsk, u64 cputime)
> > > > >  {
> > > > >  	struct cpuacct *ca;
> > > > > +	int index;
> > > > > +
> > > > > +	if (user_mode(task_pt_regs(tsk)))
> > > > > +		index = CPUACCT_USAGE_USER;
> > > > > +	else
> > > > > +		index = CPUACCT_USAGE_SYSTEM;
> >
> > This is oopsing because PowerPC task_pt_regs() returns NULL for
> > kernel threads.
> 
Thanks for notice it.

> Ah, so sometihng like:
> 
> 	struct pt_regs *regs = task_pt_regs();
> 	int index = CPUACCT_USAGE_SYSTEM;
> 
> 	if (regs && user_mode(regs))
> 		index = CPUACCT_USAGE_USER;
> 
> should work, right?
> 
Thanks, I'll confirm it in a Power7 VM from buildroot.
(maybe need some hours or till tomorrow in a poor pc...)

Btw, I reproduced this bug in above vm.

Thanks
Zhaolei


>