====== Some notes on running Linux under z/VM ======

There's nothing much to say besides what the tutorial''[1]'' tells us. Nevertheless, there are quite a few notes I took just not to let me completely forget about them, later. 

===== CPU's =====

I won't lie to you: it's insufferably slow. And for a good reason: you are virtualising twice, and the first level (Hercules) has zero paravirt. as s390x is a completely different architecture. But, maybe -- I said //maybe// -- you can suffer less, giving the VM more CPU's. So, here's how it's done: 

When creating the profile, you probably specified 4 max CPU's (''MACHINE ESA 4''). But that's it, when the machine is actually IPL'd, it goes up with only one. 

So, you take ''vmcp'', a neat little application which let you issue CP/CMS commands from inside Linux and do as follows ''[2]'': 
<code>
vmcp define cpu 02 type cp
</code>

There are other types of CPU other than CP''[3]'', like: 
<code>
CP
    indicates the central processor.
IFL
    indicates the IBM® Integrated Facility for Linux.
ZAAP
    indicates the IBM zEnterprise® Application Assist Processor.
ZIIP
    indicates the IBM z Integrated Information Processor.
ICF
    indicates the Internal Coupling Facility. 
</code>

But CP is the general kind. And I don't think we should bother much about IFL or others when running z/VM inside an emulated mainframe. 

Well, now your VM got a new CPU. It's offline, though: 
<code>
vmcp q v cpus
CPU 01  ID  FF0288F728288000 CP   CPUAFF ON
CPU 02  ID  FF0288F728288000 STOPPED CP   CPUAFF ON
[...]
</code>

Tell the guest to rescan for CPU's, by issuing ''chcpu -r''. If it don't come online (i.e. still ofline in ''lscpu -ae''), do this: ''chcpu -e 02''. And it'll probably come online. 

===== References =====

  - {{ :zvm_install_guide.pdf |}}
  - [[https://www.ibm.com/support/pages/dynamically-adding-or-removing-cpus-linux-zvm-guest|Dynamically adding or removing CPU's on Linux z/VM guests]]
  - [[https://www.ibm.com/support/knowledgecenter/SSB27U_6.4.0/com.ibm.zvm.v640.hcpb7/defincpu.htm|DEFINE CPU]]