Re: Debian CPU limitation?

2017-03-25 Thread Ray Mansell 

Thank you...

Ray

On 3/25/2017 13:52, Philipp Kern wrote:

On 03/22/2017 01:06 PM, Christian Borntraeger wrote:

On 03/22/2017 12:51 PM, Ray Mansell wrote:

Thank you all for the information. It would appear we are stuck with 32
CPUs for the moment and, since I'm retiring at the end of next week, I
guess my replacement will have to decide how to proceed :-)

As a last duty, can you maybe open a bug against Debian to bump the
max number of CPUs?

This is now Debian bug #858731.

Kind regards
Philipp Kern

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Re: Debian CPU limitation?

2017-03-25 Thread Philipp Kern 
On 03/22/2017 01:06 PM, Christian Borntraeger wrote:
> On 03/22/2017 12:51 PM, Ray Mansell wrote:
>> Thank you all for the information. It would appear we are stuck with 32
>> CPUs for the moment and, since I'm retiring at the end of next week, I
>> guess my replacement will have to decide how to proceed :-)
> As a last duty, can you maybe open a bug against Debian to bump the
> max number of CPUs?

This is now Debian bug #858731.

Kind regards
Philipp Kern

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Re: Debian CPU limitation?

2017-03-22 Thread Christian Borntraeger 
On 03/22/2017 12:51 PM, Ray Mansell wrote:
> Thank you all for the information. It would appear we are stuck with 32
> CPUs for the moment and, since I'm retiring at the end of next week, I
> guess my replacement will have to decide how to proceed :-)
>
> Thanks again,
> Ray

As a last duty, can you maybe open a bug against Debian to bump the
max number of CPUs?

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Re: Debian CPU limitation?

2017-03-22 Thread Ray Mansell 

Thank you all for the information. It would appear we are stuck with 32
CPUs for the moment and, since I'm retiring at the end of next week, I
guess my replacement will have to decide how to proceed :-)

Thanks again,
Ray

On 3/21/2017 18:46, Mark Post wrote:

On 3/21/2017 at 06:32 PM, Ray Mansell  wrote:

cat /proc/cmdline
root=/dev/disk/by-path/ccw-0.0.9207-part3 BOOT_IMAGE=0

Can this be modified to allow >32 CPUs?

If Christian is right (and he almost certainly is), then the only thing that 
will allow you to have more than 32 CPUs is to recompile the kernel with 
CONFIG_NR_CPUS set to a higher value.  I just looked at one of my SLES12 test 
systems, and we have CONFIG_NR_CPUS=256 specified, so I'm guessing having a lot 
of headroom won't cause any problems.


Mark Post

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Re: Debian CPU limitation?

2017-03-22 Thread Christian Ehrhardt 
On Tue, Mar 21, 2017 at 11:46 PM, Mark Post  wrote:

> I just looked at one of my SLES12 test systems, and we have
> CONFIG_NR_CPUS=256 specified, so I'm guessing having a lot of headroom
> won't cause any problems.


I agree,
Ubuntu has the same 256 and IIRC RH as well.
I think you only waste some memory space, but IIRC the majority of this
effect (if important to anybody) can be kept under control via maxcpus &
possible_cpus kernel parms [1].
OTOH even 256 can be too low if you are lucky enough to have a fully
fledged z13 it is 144*2SMT right - although the cases to run all that in a
single LPAR might be low enough to not care (yet) ?

[1]: https://lwn.net/Articles/537570/

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Christian Ehrhardt
Software Engineer, Ubuntu Server
Canonical Ltd

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Re: Debian CPU limitation?

2017-03-21 Thread Mark Post 
>>> On 3/21/2017 at 06:32 PM, Ray Mansell  wrote: 
> cat /proc/cmdline
> root=/dev/disk/by-path/ccw-0.0.9207-part3 BOOT_IMAGE=0
> 
> Can this be modified to allow >32 CPUs?

If Christian is right (and he almost certainly is), then the only thing that 
will allow you to have more than 32 CPUs is to recompile the kernel with 
CONFIG_NR_CPUS set to a higher value.  I just looked at one of my SLES12 test 
systems, and we have CONFIG_NR_CPUS=256 specified, so I'm guessing having a lot 
of headroom won't cause any problems.


Mark Post

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Re: Debian CPU limitation?

2017-03-21 Thread Ray Mansell 

On 3/21/2017 17:38, Mark Post wrote:

What does /proc/cmdline show for the kernel parms?


Mark Post


cat /proc/cmdline
root=/dev/disk/by-path/ccw-0.0.9207-part3 BOOT_IMAGE=0

Can this be modified to allow >32 CPUs?

Many thanks for your help,
Ray

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Re: Debian CPU limitation?

2017-03-21 Thread Christian Borntraeger 
On 03/21/2017 09:05 PM, Ray Mansell wrote:
> We've been running some beefy Debian servers, but of course one of them
> was not beefy enough, and we were asked if we could increase the number
> of CPUs from 32 to 48. Easy, I thought, until I rebooted the beefier
> server only to discover it had restricted itself to 32 CPUs, even though
> it knew 48 were present:
>
>cpu: 48 configured CPUs, 0 standby CPUs
>Brought up 32 CPUs
>
> The output from uname is:
>
>uname -a
>Linux linux02 3.16.0-4-s390x #1 SMP Debian 3.16.7-ckt9-3
>(2015-04-23) s390x GNU/Linux
>
> And it is running on a z/VM 6.3 host.
>
> I've searched through many documents and publications, but haven't been
> able to find anything that might help resolve this situation. Can anyone
> provide some insight, please?

Looks like the Debian kernel config for 3.16 contains
CONFIG-NR_CPUS=32.

This probably has made some sense in 31bit times (so that cpumasks in the
kernel could fit into a word size) but it looks like it was not increased
for 64bit to a higher value.

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Re: Debian CPU limitation?

2017-03-21 Thread Mark Post 
>>> On 3/21/2017 at 04:05 PM, Ray Mansell  wrote: 
> We've been running some beefy Debian servers, but of course one of them
> was not beefy enough, and we were asked if we could increase the number
> of CPUs from 32 to 48. Easy, I thought, until I rebooted the beefier
> server only to discover it had restricted itself to 32 CPUs, even though
> it knew 48 were present:
-snip-
> I've searched through many documents and publications, but haven't been
> able to find anything that might help resolve this situation. Can anyone
> provide some insight, please?

What does /proc/cmdline show for the kernel parms?


Mark Post

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