HP vPars and Integrity Virtual Machines V6.1 Administrator Guide

In addition to the VSP memory overhead, individual vPars and VMs have a memory overhead
depending on their size. A rough estimation of the individual guest memory overhead can be done
using the following formula:
Guest memory overhead = cpu_count * (guest_mem * 0.4% + 64M)
Where:
guest_mem is the guest (vPar/VM) memory size
cpu_count is 1 for vPar and num_vcpus for VM. (Memory overhead in a vPar is independent
of number of cpus in a vPar) .
For example, a 16G 4vCPU VM, the overhead is roughly about 512M. For the same 16G VM
with 1 vCPU, it would be around 128M. For a 16G, 16 cpu vPar, as well as a 16G, 1 CPU vPar,
memory overhead would be 128M.
When you create a 16G 4vCPU VM, additional 512M is used up by the VM. This memory is
taken from the vPar/VM pool. Note that there may be some amount of memory taken up from the
VSP memory when a vPar or VM is started. However, that is in most cases negligible compared
to the vPar/VMoverhead memory taken up from the vPar/VM pool.
The hpvmstatus –s command output has additional information displayed to take into account
the guest memory overhead required. In the following example:
# hpvmstatus –s
…
Available memory for vPars and VMs = 24320 Mbytes
Available memory for 7 (max avail.) CPU VM = 23552 Mbytes
Available memory for 7 (max avail.) CPU vPar = 24192 Mbytes
…
Although available memory in the vPar/VM memory pool is 24320 MB, if you want to create a
7 vCPU VM with all the available memory, the VM can be created only with 23552 MB. The
difference is the overhead memory required for a 7vCPU 23552MB VM. Note that the numbers
shown in hpvmstatus display are approximate and the actual memory allowed to create a VM
might have slight variations.
2.6 Hyperthreading setting on the VSP
By default, the VSP has the hyperthreading (firmware setting) ON in the npartition or server;
whereas lcpu_attr is OFF in the VSP. This setting provides optimal performance and
responsiveness for the VSP. HP strongly discourages changing the default hyperthreading settings
in the VSP, unless it is recommended in the documentation or there is some other compelling reason
to do so.
Hyperthreading is supported in individual vPars. The setboot command in individual vPars shows
that HT is ON. You can turn on lcpu_attr in individual vPars using the kctune command. By
default, lcpu_attr is OFF in the vPar (default behavior of HP-UX). Note that even when
lcpu_attr is OFF in the VSP, each vPar can have its individual lcpu_attr enabled to get
hyperthreading functionality in the vPar.
As in previous releases, hyperthreading is not supported for VMs. Therefore, individual VMs will
not show any hyperthreading capability.
2.7 VSP I/O configuration
To map direct I/O devices between the VSP and the vPars or VMs:
• From the VSP:
# hpvmdevinfo -P vm
• From the vPar or VM:
# hpvmdevinfo
32 Installing and configuring VSP for HP-UX vPars and Integrity VM V6.1