Re: [Bug #12650] Strange load average and ksoftirqd behavior with 2.6.29-rc2-git1

Ingo Molnar
2009-02-15T11:01:04Z

* Damien Wyart <damien.wyart-GANU6spQydw@public.gmane.org> wrote:

> So I followed the tracing steps in the tutorial (with the 1 sec sleep),
> which gave me this:
> http://damien.wyart.free.fr/trace_2.6.29-rc5_ksoftirqd_prob.txt.gz

thanks. There's definitely some weirdness visible in the trace,
for example:

0) gpm-1879 => ksoftir-4
------------------------------------------

0) 0.964 us | finish_task_switch();
0) ! 1768184 us | }
0) | do_softirq() {
0) | __do_softirq() {
0) | rcu_process_callbacks() {

the 1.7 seconds 'overhead' there must be a fluke - you'd notice it if
ksoftirqd _really_ took that much time to execute.

One possibility for these symptoms would be broken scheduler timestamps.
Could you enable absolute timestamp printing via:

echo funcgraph-abstime > trace_options

Also, my guess is that if you boot via idle=poll, the symptoms go away.
This would strengthen the suspicion that it's scheduler-clock troubles.

Ingo