Re: nohz and strange sleep latencies

[Thomas Gleixner <tglx@linutronix.de>]

On Thu, 22 Nov 2007, Pavel Machek wrote:
> > but perhaps somehow we miss this fact and fail to turn off the lapic 
> > clockevents drivers?
> 
> Ok, I guess I'm lost. If I offline second CPU, I immediately get
> 1000Hz timer tick... is that expected?

Hmm. No. I have no idea why this is happening.

34196 total events, 55.083 events/sec
echo 0 >/sys/devices/system/cpu/cpu1/online
36073 total events, 54.679 events/sec

> I'm trying to decide when system is idle (lets say that means "no user
> task is scheduled to wakeup within 10 seconds)... I added some
> instrumentation to nohz subsystem, but it does not behave like I'd
> expect: even if I run "while true; do sleep .01; done" loop, I see
> nohz preparing for 5 seconds sleep... while it seems obvious that it
> can only be 10msec sleep, and with max_cstate=1, it works that
> way... Plus, nte->start_pid seems to contain some random numbers :-(.
> 
> What am I doing wrong?
> 
> (Patch for illustration, I can generate full diff against vanilla,
> but...)

Just to make sure what we are hunting: Do you have the same problem
with an non-pavel-tainted 2.6.24-rc3 ?

     tglx