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

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Date:	Thu, 1 Oct 2009 15:31:05 -0700
From:	Greg KH <greg@...ah.com>
To:	Michael Abbott <michael@...neidae.co.uk>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Johan van Baarlen <jf@...baarlen.demon.nl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jan Engelhardt <jengelh@...ozas.de>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	stable@...nel.org
Subject: Re: [stable] [GIT PULL] cputime tree

On Thu, Sep 24, 2009 at 08:49:10PM +0100, Michael Abbott wrote:
> 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).

Thanks, I've queued this up for .30 and .31 stable kernels.

greg k-h
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