linux-kernel - Re: [GIT PULL] cputime tree

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Date:	Thu, 24 Sep 2009 09:51:06 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Martin Schwidefsky <schwidefsky@...ibm.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Michael Abbott <michael@...neidae.co.uk>,
	Jan Engelhardt <jengelh@...ozas.de>,
	Johan van Baarlen <jf@...baarlen.demon.nl>, stable@...nel.org
Subject: Re: [GIT PULL] cputime tree

On Thu, 24 Sep 2009 13:31:36 +0200 Martin Schwidefsky <schwidefsky@...ibm.com> wrote:

> Hi Linus,
> 
> with git commit 79741dd "idle cputime accounting" the semantic
> of the stime field of the idle processes has changed. It used to
> contain the amount of time the idle process has been scheduled.
> Since git commit 79741dd is contains the cpu time spent in the
> system by the idle process.
> 
> This change broke the output of second field of /proc/uptime. On
> systems without VIRT_CPU_ACCOUNTING the field is always zero.
> The legacy output of the field is the amount of time the idle
> process has been scheduled on cpu #0. It is good enough to
> calculate the load on an uni-processor system, it is useless
> on a multi-processor. To restore the legacy behaviour and give
> meaning to the multi-processor case the best we could come up
> with is to add the idle time over all cpus. That fixes uni-
> processors systems and gives a defined semantic on smp.
> 
> So please pull from 'cputime' branch of
> 
> 	git://git390.marist.edu/pub/scm/linux-2.6.git cputime
> 
> to receive the following updates:
> 
> Michael Abbott (1):
>       Fix idle time field in /proc/uptime
> 
>  fs/proc/uptime.c |    7 ++++++-
>  1 files changed, 6 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/proc/uptime.c b/fs/proc/uptime.c
> index 0c10a0b..766b1d4 100644
> --- a/fs/proc/uptime.c
> +++ b/fs/proc/uptime.c
> @@ -4,13 +4,18 @@
>  #include <linux/sched.h>
>  #include <linux/seq_file.h>
>  #include <linux/time.h>
> +#include <linux/kernel_stat.h>
>  #include <asm/cputime.h>
>  
>  static int uptime_proc_show(struct seq_file *m, void *v)
>  {
>  	struct timespec uptime;
>  	struct timespec idle;
> -	cputime_t idletime = cputime_add(init_task.utime, init_task.stime);
> +	int i;
> +	cputime_t idletime = cputime_zero;
> +
> +	for_each_possible_cpu(i)
> +		idletime = cputime64_add(idletime, kstat_cpu(i).cpustat.idle);
>  
>  	do_posix_clock_monotonic_gettime(&uptime);
>  	monotonic_to_bootbased(&uptime);

This is a regression fix, iirc?  One which is applicable for several 2.6.x
kernel versions?

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