Re: [git pull] scheduler changes for v2.6.26

[Ingo Molnar <mingo@elte.hu>]

* Frans Pop <elendil@planet.nl> wrote:

> > It would be nice if you could try sched-devel/latest because it has 
> > an improved ftrace "sched_switch" tracer where you can generate much 
> > longer traces of this incident. Try the new /debug/trace_entries 
> > runtime tunable.
> 
> I'll try to get the trace and will reply on the private thread we had. 
> I may need additional instructions though.

you could also reply to this thread if you dont mind, so that others can 
chime in too.

the 700-800 msecs of delays you see are very "brutal" so there must be 
something fundamentally wrong going on here.

Could you first check (under sched-devel/latest) the quality of your 
sched-clock, via running this script:

   http://people.redhat.com/mingo/cfs-scheduler/tools/watch-rq-clock.sh

if you run it, it should output ~1000 msecs periods every second:

 europe:~> watch-rq-clock.sh
 1002.115042
 1005.509851
 1004.187275
 1004.409980
 1004.430264
 1004.445508

if it's way too 'slow', say it only 100 msecs per second, then the 
scheduler clock is mis-measuring time and what the scheduler thinks to 
be a 40 msecs delay might become a 400 msecs delay.

	Ingo