Re: [Crash-utility] Running idle threads show wrong CPU numbers
Hallo Dave,
On Fri, 2010-01-22 at 09:32 -0500, Dave Anderson wrote:
----- "Michael Holzheu" <holzheu(a)linux.vnet.ibm.com>
wrote:
> Hi Dave,
>
> I have a problem with a dump where I have defined five CPUs and two of
> them are offline. In fact the logical CPUs are defined as follows:
>
> 0 on
> 1 on
> 2 off
> 3 off
> 4 on
>
> The CPU online map looks correct:
>
> crash> print/x *cpu_online_mask
> $4 = {
> bits = {0x13} ---> b10011
> }
>
> When I issue "ps" I see that all running tasks are idle, but the CPU
> numbers are not correct (0,1,2 and not 0,1,4):
>
> PID PPID CPU TASK ST %MEM VSZ RSS COMM
> > 0 0 0 800ef0 RU 0.0 0 0 [swapper]
> > 0 0 1 18c24240 RU 0.0 0 0 [swapper]
> > 0 0 2 18c2c340 RU 0.0 0 0 [swapper]
>
> I tried to debug the problem, but got stuck somewhere in "task.c". I
> think there is a problem with the idle threads initialization, where the
> online map is not considered.
>
> Maybe you can see the bug immediately. Otherwise I will have spend more
> effort for debugging that problem. I hope not :-)
Does "sys" show 5 or 3 cpus? I'm guessing it shows 3, but should show 5.
Yes it shows 3.
It looks like the s390/s390x files need to use
"get_highest_cpu_online()-1"
(like x86_64 and ppc64) in order to determine the number of cpus to account
for. As it is now, they do this, and would therefore only account for the
first 3 cpus:
int
s390x_get_smp_cpus(void)
{
return get_cpus_online();
}
int
s390_get_smp_cpus(void)
{
return get_cpus_online();
}
Hmmm ok...
When I change get_smp_cpus() to return "get_highest_cpu_online() + 1" I
see five swapper idle tasks when using "ps". The problem I now have is
that I have to provide a backtrace for the offline cpus. But the offline
CPUs do not have any stack on s390. Is there a way to tell crash that
there is no backtrace available? Probably I overlooked something...
Michael