Re: [Xenomai] two dd processes: soft lockup

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

On 08/27/2013 12:47 PM, Benedikt Boeck wrote:
> On 08/24/2013 10:42 AM, Jan Kiszka wrote:
>> On 2013-08-22 09:59, Benedikt Boeck wrote:
>>> Hello,
>>>
>>> I got a problem. After starting two dd processes (if=/dev/zero
>>> of=/dev/null), I get first a few messages about soft lockup:
>>> kernel:[...] BUG: soft lockup - CPU#. stuck for ..s! [dd:...]
>>> and little later a
>>> Kernel panic - not syncing: Fatal exception in interrupt
>>>
>>> But if I had running xeno-test before and then starting two dd processes
>>> I don't get a soft lockup. Strange?
>>>
>>> Also there is no soft lockup with a kernel identical till a deactivated
>>> CONFIG_XENOMAI.
>>> A deactivated CONFIG_SMP also prevent the error. But I like to have both
>>> cores. Trying all four variants of CONFIG_SCHED_SMT=y/n and
>>> CONFIG_SCHED_MC=y/n didn't effect the error.
>>>
>>> Tested with different kernel versions (3.4.6, 3.5.7, 3.8) always with
>>> matching ipipe patch.  I think with 3.8 I didn't get a kernel panic but
>>> still soft lockups.
>>> Using Xenomai 2.6.2.1 and haven't tried other versions yet. The
>>> processor is a Celeron Dual-Core T3100.
>>>
>>> Does somebody have a idea? Maybe I just made a simple (but effective)
>>> mistake.
>> I've tried your configuration on ipipe-3.8 [1] but wasn't able to
>> reproduced it in a 2-cpu VM with 2 dd instances. Could you provide the
>> 3.8 config as well that generates the warnings for you? And please
>> provide the information Gilles asked for,
>>
>> Thanks,
>> Jan
>>
>> [1] http://git.xenomai.org/?p=ipipe.git;a=shortlog;h=refs/heads/ipipe-3.8
>>
>>
> 
> Thanks for your replys
> 
> Tested a 3.8 kernel again. I'm using 
> http://download.gna.org/adeos/patches/v3.x/x86/ipipe-core-3.8-x86-1.patch as 
> patch. Now I'm know for sure the dd processes generate soft lockups but 
> no kernel panic occurs (running two hours). Attached todays 3.8 config.
> 
> In my VM (VirtualBox) I can't produce the error either. But the host has 
> a different CPU (Core 2 Quad Q6600, reduced numbers of cores for guest). 
> Unfortunately I haven't got another System for testing here.
> 
> Tested yesterday the 3.5.7 config with disabled CONFIG_NO_HZ: got the 
> same behavior.
> Attached content of /proc/xenomai/timer and /proc/timer_list before 
> starting dd or xeno-test (enabled NO_HZ). If needed i can also provide 
> the content after calling xeno-test.

Yes please, the contents of the kernel boot logs would help too, as well
as /proc/interrupts before and after xeno-test.

You have the HPET timer in broadcast mode, but the LAPIC timers are
started, now it would be interesting to know whether they ticked, cat
/proc/interrupts will tell us that.

-- 
                                                                Gilles.