QEMU v2.7 released

QEMU v2.7 is out! Here is a list of the highlights for KVM on z:

• Support for PCI passthrough devices is now fully functional for the first time. While we consider support as experimental, since there is still work to be done to utilize hardware acceleration facilities as well as further testing pending, attaching PCI devices directly to guests is now possible. Also note that while hot-plugging PCI devices is supported, hot-unplugging is not. Further limitations, e.g. for live guest migration, apply for now.
  We strictly recommend to use libvirt for all configuring, including PCI devices. Therefore, a step-by-step description of how to attach a PCI device to a KVM guest on z Systems will follow when the respective code becomes available in one of the next libvirt releases.
  
• Runtime instrumentation in KVM guests: IBM z13 and LinuxONE machines introduced a new hardware facility which allows to collect sampling data on code execution in CPUs at runtime. This data can be used by just-in-time compilers, like the one provided by IBM Java, to improve the generated code for better performance.
• IPL from any subchannel set: Prior to QEMU v2.7, KVM guests could only IPL/boot from devices with a subchannel set ID of 0. Once IPL'd, they could attach disks in any subchannel set just fine, but the IPL/boot from devices in subchannel sets 1-3 was not possible. With the addition of this feature, KVM guests can IPL from devices in all 4 subchannel sets.
  Here is a sample domain definition indicating the change:
  
    <disk type=’file’ device=’disk’>
      <driver name=’qemu’ type=’qcow2’/>
      <source file=’/var/lib/libvirt/images/guest.qcow2’/>
      <target dev=’vda’ bus=’virtio’/>
      <address type=’ccw’ cssid=’0xab’ ssid=’0x2’
               devno=’0x0037’/>
    </disk>

Open Positions in Development

Recently graduated (or about to do so) and looking for a job in KVM or Linux development on z Systems?
Then go to this page and search for

• 59794BR for a position in KVM on z development ("Entwickler/in für Linux Virtualisierung auf IBM z Systems"), or
• 59784BR for a position in Linux on z development ("Linux Entwickler für IBM z Systems (m/f)")

Linux kernel 4.7 released

In Linux kernel 4.7 (available here), we improved usability of the kvm_stat tool for z Systems, introducing (among others) new option -p to filter by process ID.

Using kvm_stat, one can monitor e.g. the number of SIE exits or specific diags to investigate performance issues:

  kvm statistics - summary

   Event                                        Total Current
   kvm_s390_sie_enter                          621113      96
   kvm_s390_sie_exit                           621113      96
   kvm_vcpu_wakeup                             231054      69
   kvm_s390_intercept_instruction              187720      24
   kvm_halt_poll_ns                            131133      15
   kvm_s390_handle_diag                         64543      12
   kvm_userspace_exit                            1427      11
   kvm_s390_handle_sigp                        121746       1
   kvm_set_irq                                 154402       0
   kvm_s390_handle_sigp_pei                     18407       0
   kvm_s390_handle_stsi                            12       0
   kvm_s390_handle_stfl                             1       0

Use option -p to further investigate specific QEMU processes to identify the potential culprits:

  $ ./kvm_stat -p 4304 -1 | grep kvm_s390_sie
  kvm_s390_sie_enter                              3985      3985
  kvm_s390_sie_exit                               3985      3985
  kvm_s390_sie_fault                                 0         0

Webinar: KVM for z Systems Performance

Abstract: KVM for IBM z Systems performance has not been presented at conferences before. This session covers performance aspects of the KVM host, virtual devices, and considerations for guest definitions to reach certain performance levels. It will also give examples how to monitor host and guest.
Note: It is not intended to compare KVM for IBM z Systems to other hypervisors.

Speaker: Martin Kammerer, Manager Linux on z Systems Performance Evaluation, IBM Germany

Audience: IT Managers, IT Architects, System Administrators

Date: Wednesday, July 20, 2016
Time: 11:00 AM EST / New York, 4:00 PM UK, 5:00 PM CET / Germany
Duration: 75 minutes

Registration: You can register here. After registering, you will receive a confirmation email containing information about joining the webinar.

Replay & Archive: All sessions are recorded. For the archive as well as a replay and handout of this session (available by July 25, 2016), as well as all previous webcasts please visit http://www.vm.ibm.com/education/lvc/

Contact: Please direct any questions to Stephanie Gherghe at gherghe@de.ibm.com.

KVM on z Documentation References

The amount of documentation provided in the IBM Knowledge Center can at times be overwhelming. Therefore, this entry will provide some general guidance.
See here for a continuously updated version of this entry.

The documentation for KVM on z (see overall entry point here) is grouped under these categories:

• KVM base technology: Documentation in this category relates to the latest upstream version of the respective components (mainly the kvm Linux kernel module, QEMU and libvirt).
  Note: If you are already familiar with KVM, or want to jump right in, check the KVM Virtual Server Quick Start guide: This is a cheat sheet-like 4 page document designed to get you started as quickly as possible.
• KVM for IBM z Systems: All documents in this category relate to the IBM product of the same name.

For white papers, Redbooks, live virtual classes, and more, check out the materials related to virtualization on z Systems available here.

In addition, here is a document listing the recommended limits when running KVM on z Systems. It is aimed at the KVM for IBM z product, but also provides a good starting point when running other flavors of KVM on z.

Finally, documentation and pointers on ICM (IBM Cloud Manager, IBM's OpenStack-based product) can be found here.

KVM Forum 2016

The schedule of the KVM Forum 2016, to be held August 24-26 in Toronto, is out here.
We (KVM on z project) will be hosting three sessions:

• Nesting KVM on s390x (David Hildenbrand)
• KVM on System z: The Good, the Bad and the Weird (Cornelia Huck)
• As Time Goes By, Analysing Where We Spend Our Cycles During Exits (Christian Bornträger)

qclib v1.2.0 released

New version qclib v1.2.0 was released on IBM developerWorks here.
Among others, this version adds additional counts for KVM hosts and guests as follows:

• For KVM hosts: Counts for CPs, IFLs and CPUs (sum of CPs and IFLs)
• For KVM guests: CP and IFL counts

Below is some (edited) output of the sample program qc_test (part of the library), highlighting the new attributes for a KVM host with 4 IFLs and a guest with 2 virtual IFLs. See the README for documentation and further details.

    ===== Layer 3: KVM-hypervisor ==========================
             qc_layer_type [n/a]: KVM-hypervisor
         qc_layer_category [n/a]: HOST
         qc_layer_type_num [n/a]: 6
     qc_layer_category_num [n/a]: 2
     qc_control_program_id [S  ]: KVM/Linux
             qc_adjustment [S  ]: 1000

          qc_num_cpu_total [  V]: 4
      qc_num_cpu_dedicated [SHV]: 0
         qc_num_cpu_shared [SHV]: 4
           qc_num_cp_total [ HV]: 0
       qc_num_cp_dedicated [ hV]: 0
          qc_num_cp_shared [ hV]: 0
          qc_num_ifl_total [SHV]: 4
      qc_num_ifl_dedicated [ShV]: 0
         qc_num_ifl_shared [ShV]: 4
    ===================================================

      ===== Layer 4: KVM-guest ==========================
               qc_layer_type [n/a]: KVM-guest
           qc_layer_category [n/a]: GUEST
           qc_layer_type_num [n/a]: 7
       qc_layer_category_num [n/a]: 1
               qc_layer_name [S  ]: u1604
      qc_layer_extended_name [S  ]: u1604
               qc_layer_uuid [S  ]: 407d134c-7d93-4a7b-bd27-4568ef10e85a

            qc_num_cpu_total [S  ]: 2
       qc_num_cpu_configured [S  ]: 2
          qc_num_cpu_standby [S  ]: 0
         qc_num_cpu_reserved [S  ]: 0
        qc_num_cpu_dedicated [S  ]: 0
           qc_num_cpu_shared [S  ]: 2
            qc_num_ifl_total [S  ]: 2
        qc_num_ifl_dedicated [S  ]: 0
           qc_num_ifl_shared [S  ]: 2
        qc_ifl_dispatch_type [SHV]: 3
      ===================================================

qclib is a C library providing access to system information on the various layers of virtualization on z Systems.