Re: BUG: soft lockup - CPU stuck for ...

[Robert Wimmer <r.wimmer@tomorrow-focus.de>]

Hi,

many thanks for your replys. I've upgraded
some systems to kernel 2.6.29 a few days ago.
There was especially one system which nearly always
crashed during kernel compilation. With 2.6.29
as host an guest it currently works. Have now
compiled the kernel three times (always from
scratch) and nothing crashed. 

To use i686 (or x86) as host wouldn't be a option.

The preemtible kernel seems a possible way to go
if the crash happens again. But if it works now
I'll leave it as it is since there are still drivers
out there which have problems with preemt. kernels.

But there is something I still wonder: Is this the
right mailing list for such requests? If I read a
message like "BUG: soft lockup - CPU#0 stuck for ..."?
it looks for me like a bug which should be looked after
by the develpers but it seems that nobody here really
cares for such reports. I'm really a gratefull for
KVM and the work by done by all the developers but
isn't it in the interest of a company like Redhat to
get the product stable and to eliminate all known
bugs before the release of their new virtualisation
product? I really don't mean this as flame because
my intention is really to get KVM better. But the only
thing I can do is to submit bug reports since I'm not
a C/C++ developer.

Btw: Is there a overview what kernel settings
are recommended for KVM hosts and guests beside the
obvious ones? I've learned so far that the noop
I/O scheduler in the guest and deadline in the host
are good choices. I've read in the XFS filesystem FAQ 
that the KVM "drive=" option should include "cache=none"
to avoid filesystem corruption (which I've already had
in some KVMs and caused me to switch to ext3 instead).
The kernel settings are especially usefull for people
like me who're using Gentoo where you have to compile
everything yourself.

Keep the good work going!
Thanks!
Robert




many than

> Hi,
> I was also experiencing this problem a lot for quite a long time (and for
> wide range of KVM versions..)
> I might be completely wrong as I'm not sure if it was really the reason,
> but i THINK it disappeared when I started to use fully preemptible kernel on host..
> You might want to try it...
> BR
> nik

On Sun, Mar 29, 2009 at 07:51:21AM +0000, Gerrit Slomma wrote:
> Robert Wimmer <r.wimmer <at> tomorrow-focus.de> writes:
> 
> > 
> > Hi,
> > 
> > does anyone know how to solve the problem
> > with "BUG: soft lockup - CPU#0 stuck for ..."?
> > Today I got the messages below during compilation
> > of the kernel modules in a guest. Using kvm84 and Kernel 2.6.29
> > as host kernel and 2.6.28 as guest kernel during the
> > hangup of the guest neither ssh or ping was possible.
> > After about 2 minutes the guest was reachable again
> > and I saw the messages below with "dmesg".
> > 
> > Maybe it is related with my prev. anserwed posting:
> > http://article.gmane.org/gmane.comp.emulators.kvm.devel/29677
> > 
> > Thanks!
> > Robert
> > 
> > BUG: soft lockup - CPU#0 stuck for 61s!
> > (...)
> 
> Hello
> 
> Do you use x86_64 or i686?
> Look at my post here http://article.gmane.org/gmane.comp.emulators.kvm.devel/29833
> And my Bug-report here https://bugzilla.redhat.com/show_bug.cgi?id=492688.
> I do not have the problems while running but after migrating. Problems with
> stuck CPUs vanish if i686 for the host is used - but i am testing further.
> 
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