Re: [PATCH] Fixes spurious system load spikes in /proc/loadavgrt

[Ingo Molnar <mingo@elte.hu>]

* Sven-Thorsten Dietrich <sven@thebigcorporation.com> wrote:

> On Thu, 2007-08-16 at 21:37 -0300, Luis Claudio R. Goncalves wrote:
> > Hello,
> > 
> > The values in /proc/loadavgrt are sometimes the real load and sometimes
> > garbage. As you can see in th tests below, it occurs from in 2.6.21.5-rt20 
> > to 2.6.23-rc2-rt2. The code for calc_load(), in kernel/timer.c has not
> > changed much in -rt patches.
> 
> > 
> > Signed-off-by: Luis Claudio R. Goncalves <lclaudio@uudg.org>
> > ---
> > 
> > diff --git a/kernel/sched.c b/kernel/sched.c
> > index 811a502..c61609a 100644
> > --- a/kernel/sched.c
> > +++ b/kernel/sched.c
> > @@ -2520,6 +2520,13 @@ unsigned long rt_nr_uninterruptible(void)
> >  	for_each_online_cpu(i)
> >  		sum += cpu_rq(i)->rt_nr_uninterruptible;
> >  
> > +	/*
> > +	 * Since we read the counters lockless, it might be slightly
> > +	 * inaccurate. Do not allow it to go below zero though:
> > +	 */
> > +	if (unlikely((long)sum < 0))
> > +		sum = 0;
> > +
> >  	return sum;
> >  }
> >  
> > diff --git a/linux-2.6.21.x86_64/kernel/timer.c b/linux-2.6.21.x86_64_lc/kernel/timer.c
> > index 882ca9d..0e49bf6 100644
> > --- a/linux-2.6.21.x86_64/kernel/timer.c
> > +++ b/linux-2.6.21.x86_64_lc/kernel/timer.c
> > @@ -1432,23 +1432,25 @@ unsigned long avenrun_rt[3];
> >  static inline void calc_load(unsigned long ticks)
> >  {
> >  	unsigned long active_tasks; /* fixed-point */
> > +	unsigned long active_rt_tasks; /* fixed-point */
> >  	static int count = LOAD_FREQ;
> >  
> >  	count -= ticks;
> >  	if (unlikely(count < 0)) {
> >  		active_tasks = count_active_tasks();
> > +		active_rt_tasks = count_active_rt_tasks();
> 
> Where is this used?

what is "this"? /proc/loadavg? Or the code/patch you quoted?

	Ingo