crash with CFS v4 and qemu/kvm (was: [patch] CFS scheduler, v4)

crash with CFS v4 and qemu/kvm (was: [patch] CFS scheduler, v4)

[Christian Hesse]

[-- Attachment #1: Type: text/plain, Size: 575 bytes --]

On Friday 20 April 2007, Ingo Molnar wrote:
> i'm pleased to announce release -v4 of the CFS patchset.

Hi Ingo, hi Avi, hi all,

I'm trying to use kvm-20 with cfs v4 and get a crash:

eworm@revo:~$ /usr/local/kvm/bin/qemu -snapshot /mnt/data/virtual/qemu/winxp.img
kvm_run: failed entry, reason 7
kvm_run returned -8

It works (though it is a bit slow) if I start qemu with strace, so for me it 
looks like a race condition?

I did not test any earlier versions of cfs and kvm in combination - I can't 
say if it happens there as well.
-- 
Regards,
Chris

[-- Attachment #2: This is a digitally signed message part. --]
[-- Type: application/pgp-signature, Size: 189 bytes --]

Re: crash with CFS v4 and qemu/kvm (was: [patch] CFS scheduler, v4)

[Ingo Molnar]

* Christian Hesse <mail-8oMOrB1mGocUSW6y5lq3GQ@public.gmane.org> wrote:

> On Friday 20 April 2007, Ingo Molnar wrote:
> > i'm pleased to announce release -v4 of the CFS patchset.
> 
> Hi Ingo, hi Avi, hi all,
> 
> I'm trying to use kvm-20 with cfs v4 and get a crash:
> 
> eworm@revo:~$ /usr/local/kvm/bin/qemu -snapshot /mnt/data/virtual/qemu/winxp.img
> kvm_run: failed entry, reason 7
> kvm_run returned -8
> 
> It works (though it is a bit slow) if I start qemu with strace, so for 
> me it looks like a race condition?

hm. Can you work it around with:

   echo 0 > /proc/sys/kernel/sched_granularity_ns

?

If yes then this is a wakeup race: some piece of code relies on the 
upstream scheduler preempting the waker task immediately in 99% of the 
cases.

and you might want to test -v5 too which i released earlier today. It 
has no bugfix in this area though, so it will likely still trigger this 
race - but it will also hopefully be even more pleasant to use than -v4 
;-)

	Ingo

-------------------------------------------------------------------------
This SF.net email is sponsored by DB2 Express
Download DB2 Express C - the FREE version of DB2 express and take
control of your XML. No limits. Just data. Click to get it now.
http://sourceforge.net/powerbar/db2/

Re: crash with CFS v4 and qemu/kvm (was: [patch] CFS scheduler, v4)

[Christian Hesse]

[-- Attachment #1.1: Type: text/plain, Size: 1304 bytes --]

On Monday 23 April 2007, Ingo Molnar wrote:
> * Christian Hesse <mail-8oMOrB1mGocUSW6y5lq3GQ@public.gmane.org> wrote:
> > On Friday 20 April 2007, Ingo Molnar wrote:
> > > i'm pleased to announce release -v4 of the CFS patchset.
> >
> > Hi Ingo, hi Avi, hi all,
> >
> > I'm trying to use kvm-20 with cfs v4 and get a crash:
> >
> > eworm@revo:~$ /usr/local/kvm/bin/qemu -snapshot
> > /mnt/data/virtual/qemu/winxp.img kvm_run: failed entry, reason 7
> > kvm_run returned -8
> >
> > It works (though it is a bit slow) if I start qemu with strace, so for
> > me it looks like a race condition?
>
> hm. Can you work it around with:
>
>    echo 0 > /proc/sys/kernel/sched_granularity_ns
>
> ?
>
> If yes then this is a wakeup race: some piece of code relies on the
> upstream scheduler preempting the waker task immediately in 99% of the
> cases.
>
> and you might want to test -v5 too which i released earlier today. It
> has no bugfix in this area though, so it will likely still trigger this
> race - but it will also hopefully be even more pleasant to use than -v4
> ;-)

Hi Ingo,

This was kvm's fault. It works perfectly now without modifications to the 
scheduler. If anybody is interested in details please see the kvm mailing 
list archives.
-- 
Regards,
Chris

[-- Attachment #1.2: This is a digitally signed message part. --]
[-- Type: application/pgp-signature, Size: 189 bytes --]

[-- Attachment #2: Type: text/plain, Size: 286 bytes --]

-------------------------------------------------------------------------
This SF.net email is sponsored by DB2 Express
Download DB2 Express C - the FREE version of DB2 express and take
control of your XML. No limits. Just data. Click to get it now.
http://sourceforge.net/powerbar/db2/

[-- Attachment #3: Type: text/plain, Size: 186 bytes --]

_______________________________________________
kvm-devel mailing list
kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
https://lists.sourceforge.net/lists/listinfo/kvm-devel