linux-kernel - Re: [PATCH 03/33] cputime: Generic on-demand virtual cputime accounting

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Date:	Tue, 08 Jan 2013 15:23:31 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Alessio Igor Bogani <abogani@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Chris Metcalf <cmetcalf@...era.com>,
	Christoph Lameter <cl@...ux.com>,
	Geoff Levand <geoff@...radead.org>,
	Gilad Ben Yossef <gilad@...yossef.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Li Zhong <zhong@...ux.vnet.ibm.com>,
	Namhyung Kim <namhyung.kim@....com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 03/33] cputime: Generic on-demand virtual cputime
 accounting

On Tue, 2013-01-08 at 03:08 +0100, Frederic Weisbecker wrote:

> +++ b/kernel/sched/cputime.c
> @@ -3,6 +3,7 @@
>  #include <linux/tsacct_kern.h>
>  #include <linux/kernel_stat.h>
>  #include <linux/static_key.h>
> +#include <linux/context_tracking.h>
>  #include "sched.h"
>  
> 
> @@ -495,10 +496,24 @@ void vtime_task_switch(struct task_struct *prev)
>  #ifndef __ARCH_HAS_VTIME_ACCOUNT
>  void vtime_account(struct task_struct *tsk)
>  {
> -	if (in_interrupt() || !is_idle_task(tsk))
> -		vtime_account_system(tsk);
> -	else
> -		vtime_account_idle(tsk);
> +	if (!in_interrupt()) {
> +		/*
> +		 * If we interrupted user, context_tracking_in_user()
> +		 * is 1 because the context tracking don't hook

s/don't/doesn't/

> +		 * on irq entry/exit. This way we know if
> +		 * we need to flush user time on kernel entry.

Also, the above comment is simply confusing. Why not just say something
like:

 Context tracking doesn't hook on irq entry/exit. The context will still
 be user context if the interrupt preempted user space.

No need to explain the implementation details of
"context_tracing_in_user() is 1 ...".

-- Steve

> +		 */
> +		if (context_tracking_in_user()) {
> +			vtime_account_user(tsk);
> +			return;
> +		}
> +
> +		if (is_idle_task(tsk)) {
> +			vtime_account_idle(tsk);
> +			return;
> +		}
> +	}
> +	vtime_account_system(tsk);
>  }
>  EXPORT_SYMBOL_GPL(vtime_account);
>  #endif /* __ARCH_HAS_VTIME_ACCOUNT */
> @@ -587,3 +602,72 @@ void thread_group_cputime_adjusted(struct task_struct *p, cputime_t *ut, cputime
>  	cputime_adjust(&cputime, &p->signal->prev_cputime, ut, st);
>  }
>  #endif


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