linux-kernel - Re: [PATCH v2] fix idle ticks in cpu summary line of /proc/stat

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Date:	Wed, 18 Jul 2012 13:52:55 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	Michal Hocko <mhocko@...e.cz>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] fix idle ticks in cpu summary line of /proc/stat

On Tue, 13 Mar 2012 14:02:35 +0530
"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com> wrote:

> On 03/13/2012 01:37 PM, Michal Hocko wrote:
> 
> > OK, so the updated version of the patch looks like this. I am sorry but
> > I had time to only compile test this...
> > ---
> > From d12247f14c5f8b00ae97a87442f62e49227a759b Mon Sep 17 00:00:00 2001
> > From: Michal Hocko <mhocko@...e.cz>
> > Date: Mon, 12 Mar 2012 13:11:38 +0100
> > Subject: [PATCH] nohz: fix idle ticks in cpu summary line of /proc/stat
> > 
> > Git commit 09a1d34f8535ecf9 "nohz: Make idle/iowait counter update
> > conditional" introduced a bug in regard to cpu hotplug. The effect is
> > that the number of idle ticks in the cpu summary line in /proc/stat is
> > still counting ticks for offline cpus.
> > 
> > Reproduction is easy, just start a workload that keeps all cpus busy,
> > switch off one or more cpus and then watch the idle field in top.
> > On a dual-core with one cpu 100% busy and one offline cpu you will get
> > something like this:
> > 
> > %Cpu(s): 48.7 us,  1.3 sy,  0.0 ni, 50.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
> > 
> > The problem is that an offline cpu still has ts->idle_active == 1.
> > To fix this we should make sure that the cpu is online when calling
> > get_cpu_idle_time_us and get_cpu_iowait_time_us.
> > 
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: "Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
> > Reported-by: Martin Schwidefsky <schwidefsky@...ibm.com>
> > Signed-off-by: Michal Hocko <mhocko@...e.cz>
> > ---
> >  fs/proc/stat.c |   14 ++++++++++----
> >  1 files changed, 10 insertions(+), 4 deletions(-)
> > 
> > diff --git a/fs/proc/stat.c b/fs/proc/stat.c
> > index 121f77c..62bda24 100644
> > --- a/fs/proc/stat.c
> > +++ b/fs/proc/stat.c
> > @@ -24,10 +24,13 @@
> > 
> >  static u64 get_idle_time(int cpu)
> >  {
> > -	u64 idle, idle_time = get_cpu_idle_time_us(cpu, NULL);
> > +	u64 idle, idle_time = -1ULL;
> > +
> > +	if (cpu_online(cpu))
> > +		idle_time = get_cpu_idle_time_us(cpu, NULL);
> > 
> >  	if (idle_time == -1ULL) {
> > -		/* !NO_HZ so we can rely on cpustat.idle */
> > +		/* !NO_HZ or cpu offline so we can rely on cpustat.idle */
> >  		idle = kcpustat_cpu(cpu).cpustat[CPUTIME_IDLE];
> >  		idle += arch_idle_time(cpu);
> >  	} else
> > @@ -38,10 +41,13 @@ static u64 get_idle_time(int cpu)
> > 
> >  static u64 get_iowait_time(int cpu)
> >  {
> > -	u64 iowait, iowait_time = get_cpu_iowait_time_us(cpu, NULL);
> > +	u64 iowait, iowait_time = -1ULL;
> > +
> > +	if (cpu_online(cpu))
> > +		iowait_time = get_cpu_iowait_time_us(cpu, NULL);
> > 
> >  	if (iowait_time == -1ULL)
> > -		/* !NO_HZ so we can rely on cpustat.iowait */
> > +		/* !NO_HZ or cpu offline so we can rely on cpustat.iowait */
> >  		iowait = kcpustat_cpu(cpu).cpustat[CPUTIME_IOWAIT];
> >  	else
> >  		iowait = usecs_to_cputime64(iowait_time);
> 
> 
> 
> Yeah, this looks much better..
> 
> Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>

What happened to this patch? The fix for s390 (git commit cb85a6ed67e979c59
"proc: stats: Use arch_idle_time for idle and iowait times if available"
is upstream but the fix for non-s390 systems is missing, no?

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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