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

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Message-ID: <alpine.DEB.1.10.0909242047280.7033@venus.araneidae.co.uk>
Date:	Thu, 24 Sep 2009 20:49:10 +0100 (BST)
From:	Michael Abbott <michael@...neidae.co.uk>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	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, Andrew Morton wrote:
> 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?

Yes indeed, all since the regression was introduced I think around about 
.28 (though I seem to remember having to tweak the code a little when 
rebasing it forward).
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