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Samuel Torton

2006-Jan-24 11:10 UTC

[Xen-users] domU machines hang when Hyperthreading enabled in BIOS

Hi,

I can''t get rid of an annoying domU machines hanging issue with
Hyperthreading enabled in my BIOS.

Hardware config: IBM x325 series
                 2 * CPUs Intel Xeon 3.06 Ghz

Xen version:     3.0.0
Kernel version:  2.6.12.6
Linux distrib:   Debian Sarge 3.1 r1

I run 1 domU machine on my dom0, here is my Xen config:
  . xen0:
   /etc/xen/xend-config.sxp : (dom0-num-cpus 0)
  . xenU:
   /etc/xen/myxenU.cfg      : vcpus = 2


- First case:  . BIOS Hyperthreading : DISABLED
               . xen0 kernel config  : SMT enabled
               . xenU kernel config  : SMT enabled or disabled (whatever)
  When I reboot the physical machine, and run the command "xm list" :
   . dom0 is visible and works fine
     --> I see 2 cpus.
   . domU is visible and works fine
     --> I see 2 cpus;
         I can console the xenU machine and work inside.

- Second case: . BIOS Hyperthreading : ENABLED
               . xen0 kernel config  : SMT enabled
               . xenU kernel config  : SMT enabled or disabled (whatever)
  --> When I reboot the physical machine, and run the command "xm
list" :
   . dom0 is visible and works fine
      --> I see 4 cpus.
   . domU is visible and SEEMS to work fine (!)
      --> I see 2 cpus;
          If I console the xenU machine, I see the machine
          has booted but is hanged before finishing the boot !!! :-(

Would you have any idea, any clue ? Do you have any experience ?
  - Where to search in log files in order to detect the problem ?
  - Which kernel parameter would I have forgotten ?
  - I don''t even know whether the problem comes from xen0 or xenU
kernel
conf !
  - etc... ?

Thank you in advance...
... please, don''t advise me I have to disable Hyperthreading in BIOS
!;-)

Regards,
Samuel


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Vincent Hanquez

2006-Jan-24 14:32 UTC

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Re: [Xen-users] domU machines hang when Hyperthreading enabled in BIOS

On Tue, Jan 24, 2006 at 12:10:12PM +0100, Samuel Torton
wrote:> I can''t get rid of an annoying domU machines hanging issue with
> Hyperthreading enabled in my BIOS.
it seems we have lots of random issues with HT, please can you add your
information at the end of bug 432, so that nothing get lost ?

http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=432
> - First case:  . BIOS Hyperthreading : DISABLED
>                . xen0 kernel config  : SMT enabled
>                . xenU kernel config  : SMT enabled or disabled (whatever)
>   When I reboot the physical machine, and run the command "xm
list" :
>    . dom0 is visible and works fine
>      --> I see 2 cpus.
>    . domU is visible and works fine
>      --> I see 2 cpus;
>          I can console the xenU machine and work inside.
> 
> - Second case: . BIOS Hyperthreading : ENABLED
>                . xen0 kernel config  : SMT enabled
>                . xenU kernel config  : SMT enabled or disabled (whatever)
>   --> When I reboot the physical machine, and run the command "xm
list" :
>    . dom0 is visible and works fine
>       --> I see 4 cpus.
>    . domU is visible and SEEMS to work fine (!)
>       --> I see 2 cpus;
>           If I console the xenU machine, I see the machine
>           has booted but is hanged before finishing the boot !!! :-(
please provide both bootlog; to know exactly where it hangs is good to
know for us.
> Would you have any idea, any clue ? Do you have any experience ?
>   - Where to search in log files in order to detect the problem ?
>   - Which kernel parameter would I have forgotten ?
>   - I don''t even know whether the problem comes from xen0 or xenU
kernel
> conf !
this is probably not a configuration problem.
> Thank you in advance...
> ... please, don''t advise me I have to disable Hyperthreading in
BIOS !;-)
I''m no fan of HT, that what I''ld do on any personal HT cpu
I''ld have ;)

-- 
Vincent Hanquez

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Anand

2006-Jan-25 14:02 UTC

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Re: [Xen-users] domU machines hang when Hyperthreading enabled in BIOS

Are the errors appearing on all HT machines ? Is there a defined pattern in
these errors ?

The reason i am asking is because i plan to use a dual xeon 3.0 HT as my
production machine. I don''t have one now hence i can''t test on
it now :(

Anyone else on the list with HT experience ?

--

regards,

Anand


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Ernst Bachmann

2006-Jan-25 14:34 UTC

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Re: [Xen-users] domU machines hang when Hyperthreading enabled in BIOS

On Wednesday 25 January 2006 15:02, Anand wrote:> Are the errors appearing on all HT machines ? Is there a defined pattern in
> these errors ?
>
> The reason i am asking is because i plan to use a dual xeon 3.0 HT as my
> production machine. I don''t have one now hence i can''t
test on it now :(
>
> Anyone else on the list with HT experience ?
I''m running two servers with dual Xeons, HT enabled, EM64T enabled, one
with
4GB, one with 8GB Ram under xen.
Works without major problems, except for a faulty SCSI driver (which fails 
under plain linux, too) and "irq 18 occured, noone cared" kernel
messages
when attaching/detaching USB devices.

MB is from Supermicro.

Some older boxes (2GB Ram, dual Xeon without EM64T but with HT enabled) are 
working nicely under xen, too.

/Ernst

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Anand

2006-Jan-25 14:38 UTC

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Re: [Xen-users] domU machines hang when Hyperthreading enabled in BIOS

Thanks Mats, Ernst.

--

regards,

Anand


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Samuel Torton

2006-Jan-25 15:08 UTC

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RE: [Xen-users] domU machines hang when Hyperthreading enabled in BIOS

Hi,


I found the solution (or workaround only ?) to prevent from hanging up xenU
machines on a xen0 + BIOS HT enabled.

I must say I had another issue with the previous I described yesterday (see
thread).
I couldn''t set up the max number of CPUs for my xen0 machine.
Whatever the "(dom0-cpus)" parameter value in my
/etc/xen/xend-config.sxp
config file, I always had the following result in the "xm list"
command
line:
   > vn2:~# xm list
   > Name        ID Mem(MiB) VCPUs State  Time(s)
   > Domain-0    0      500     4 r-----   967.6
It was not possible for me to set up a max number value of CPUs on my dom0,
it was always set to the MAX (ie. 2 proc + HT enabled = 4 CPUs)

Thus, I added the following parameter in my GRUB/menus.lst config file:
"maxcpus=N"
example:
  module /vmlinuz-2.6-xen0 root=/dev/sda3 ro maxcpus=3 console=tty0
max_loop=32

Then I rebooted.
... and suddenly my both problems where solved:

-1- I can limit my number of CPUs to a maximum value for xen0 and xenU
machines;
-2- My xenU stopped hanging up on boot !
    (I must say it was not a kernel panic, but just a hang up... can''t
explain it)


However, now I have some other inherent questions:

- I cannot set dynamically number of CPUs on my xen0 machine when it runs,
  ie. the command "xm vcpu-set 0 N" doesn''t work !
  (whereas it works for xenU machines)
  --> is it normal ?
      is it possible in theory to change that number of CPUs on a running
xen0 ?

- What''s the difference between (dom0-num-cpus) and (dom0-cpus) ?
  Which one is really correct ?
  Is it (dom0-num-cpus) for Xen2 and (dom0-cpus) for Xen3 ?

- Whatever the value I give to my "(dom0-cpus)" parameter in my
  /etc/xen/xend-config.sxp file, it''s totally unuseful... I really
don''t
know
  what''s the influence of this parameter to my machines ???


That''s why I''m wondering whether I really found the solution
to my previous
problem, or if it''s only a workaround ?



Thank you,
Samuel






-----Original Message-----
From: xen-users-bounces@lists.xensource.com
[mailto:xen-users-bounces@lists.xensource.com]On Behalf Of Samuel Torton
Sent: Tuesday, January 24, 2006 12:10 PM
To: xen-users@lists.xensource.com
Subject: [Xen-users] domU machines hang when Hyperthreading enabled in
BIOS


Hi,

I can''t get rid of an annoying domU machines hanging issue with
Hyperthreading enabled in my BIOS.

Hardware config: IBM x325 series
                 2 * CPUs Intel Xeon 3.06 Ghz

Xen version:     3.0.0
Kernel version:  2.6.12.6
Linux distrib:   Debian Sarge 3.1 r1

I run 1 domU machine on my dom0, here is my Xen config:
  . xen0:
   /etc/xen/xend-config.sxp : (dom0-num-cpus 0)
  . xenU:
   /etc/xen/myxenU.cfg      : vcpus = 2


- First case:  . BIOS Hyperthreading : DISABLED
               . xen0 kernel config  : SMT enabled
               . xenU kernel config  : SMT enabled or disabled (whatever)
  When I reboot the physical machine, and run the command "xm list" :
   . dom0 is visible and works fine
     --> I see 2 cpus.
   . domU is visible and works fine
     --> I see 2 cpus;
         I can console the xenU machine and work inside.

- Second case: . BIOS Hyperthreading : ENABLED
               . xen0 kernel config  : SMT enabled
               . xenU kernel config  : SMT enabled or disabled (whatever)
  --> When I reboot the physical machine, and run the command "xm
list" :
   . dom0 is visible and works fine
      --> I see 4 cpus.
   . domU is visible and SEEMS to work fine (!)
      --> I see 2 cpus;
          If I console the xenU machine, I see the machine
          has booted but is hanged before finishing the boot !!! :-(

Would you have any idea, any clue ? Do you have any experience ?
  - Where to search in log files in order to detect the problem ?
  - Which kernel parameter would I have forgotten ?
  - I don''t even know whether the problem comes from xen0 or xenU
kernel
conf !
  - etc... ?

Thank you in advance...
... please, don''t advise me I have to disable Hyperthreading in BIOS
!;-)

Regards,
Samuel


_______________________________________________
Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users


_______________________________________________
Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

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