linux-kernel - Re: [PATCH 3/3] cputime: Consolidate cputime adjustment code

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Message-ID: <20121125190909.GA1866@windriver.com>
Date:	Sun, 25 Nov 2012 14:09:09 -0500
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 3/3] cputime: Consolidate cputime adjustment code

[[PATCH 3/3] cputime: Consolidate cputime adjustment code] On 23/11/2012 (Fri 15:21) Frederic Weisbecker wrote:

> task_cputime_adjusted() and thread_group_cputime_adjusted()
> essentially share the same code. They just don't use the same
> source:
> 
> * The first function uses the cputime in the task struct and the
> previous adjusted snapshot that ensures monotonicity.
> 
> * The second adds the cputime of all tasks in the group and the
> previous adjusted snapshot of the whole group from the signal
> structure.
> 
> Just consolidate the common code that does the adjustment. These
> functions just need to fetch the values from the appropriate
> source.
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> ---
>  include/linux/sched.h  |    9 +++++++--
>  kernel/fork.c          |    2 +-
>  kernel/sched/cputime.c |   46 +++++++++++++++++++++++-----------------------
>  3 files changed, 31 insertions(+), 26 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index e75cab5..d23204f 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -433,6 +433,11 @@ struct cpu_itimer {
>  	u32 incr_error;
>  };
>  
> +struct cputime {
> +	cputime_t utime;
> +	cputime_t stime;
> +};
> +

Hi Frederic,

This new struct cputime is a 2/3 subset of the three variable struct
task_cputime we see right below.  Maybe this is a stupid question, but I
was wondering why you didn't re-use task_cputime, and ignore the
sum_exec_runtime field -- vs. introducing this very similar struct?

Or maybe there is another way to consolidate the structs?  With the
two being so similar, I wonder if it will be confusing when to use which
one of the two.

Thanks,
Paul.
--

/**
 * struct task_cputime - collected CPU time counts
 * @utime:		time spent in user mode, in &cputime_t units
 * @stime:              time spent in kernel mode, in &cputime_t units
 * @sum_exec_runtime:   total time spent on the CPU, in nanoseconds
 *
 * This structure groups together three kinds of CPU time that are
 * tracked for threads and thread groups.  Most things considering
 * CPU time want to group these counts together and treat all three
 * of them in parallel.
 */
struct task_cputime {
        cputime_t utime;
        cputime_t stime;
        unsigned long long sum_exec_runtime;
};

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