SUSE Best Practices for SAP HANA on KVM #

This best practice document describes how SUSE Linux Enterprise Server for SAP Applications 15 SP2 with KVM should be configured to run SAP HANA for use in production environments. The setup of the SAP HANA system or other components like HA clusters are beyond the scope of this document.

The following sections describe how to set up and configure the three KVM components required to run SAP HANA on KVM:

Follow Section 2, “Supported scenarios and prerequisites” and the respective SAP Notes to ensure a supported configuration. Most of the configuration options are specific to the libvirt package and therefore require modifying the VM guest’s domain XML file.

Follow the SUSE Best Practices for SAP HANA on KVM - SUSE Linux Enterprise Server for SAP Applications 15 SP2 document at hand which describes the steps necessary to create a supported SAP HANA on KVM configuration. SUSE Linux Enterprise Server for SAP Applications must be used for both hypervisor and guest.

Inquiries about scenarios not listed here should be directed to saphana@suse.com.

The following sections describe how to set up and configure the hypervisor for a virtualized SAP HANA scenario.

zypper in -t pattern kvm_server kvm_tools

lspci -vs 17:00.0
17:00.0 Ethernet controller: Intel Corporation Ethernet Controller X710 for 10GbE SFP+ (rev 01)
        Subsystem: Intel Corporation Ethernet Converged Network Adapter X710-2
        Flags: bus master, fast devsel, latency 0, IRQ 247, NUMA node 0
        Memory at 9c000000 (64-bit, prefetchable) [size=8M]
        Memory at 9d008000 (64-bit, prefetchable) [size=32K]
        Expansion ROM at 9d680000 [disabled] [size=512K]
        Capabilities: [40] Power Management version 3
        Capabilities: [50] MSI: Enable- Count=1/1 Maskable+ 64bit+
        Capabilities: [70] MSI-X: Enable+ Count=129 Masked-
        Capabilities: [a0] Express Endpoint, MSI 00
        Capabilities: [e0] Vital Product Data
        Capabilities: [100] Advanced Error Reporting
        Capabilities: [140] Device Serial Number d8-ef-c3-ff-ff-fe-fd-3c
        Capabilities: [150] Alternative Routing-ID Interpretation (ARI)
        Capabilities: [160] Single Root I/O Virtualization (SR-IOV)
        Capabilities: [1a0] Transaction Processing Hints
        Capabilities: [1b0] Access Control Services
        Capabilities: [1d0] #19
        Kernel driver in use: i40e
        Kernel modules: i40e

echo 4 > /sys/bus/pci/devices/0000\:17\:00.0/sriov_numvfs

echo 4 > /sys/class/net/eth10/device/sriov_numvfs

[Unit]
Description=/etc/init.d/after.local Compatibility
After=libvirtd.service
Requires=libvirtd.service
[Service]
Type=oneshot
ExecStart=/etc/init.d/after.local
RemainAfterExit=true

[Install]
WantedBy=multi-user.target

#! /bin/sh
#
# Copyright (c) 2010 SuSE LINUX Products GmbH, Germany.  All rights reserved.
# ...
echo 4 > /sys/class/net/eth10/device/sriov_numvfs

lspci | grep -i "Fibre Channel"
85:00.0 Fibre Channel: QLogic Corp. ISP2722-based 16/32Gb Fibre Channel to PCIe Adapter (rev 01)
85:00.1 Fibre Channel: QLogic Corp. ISP2722-based 16/32Gb Fibre Channel to PCIe Adapter (rev 01)
ad:00.0 Fibre Channel: QLogic Corp. ISP2722-based 16/32Gb Fibre Channel to PCIe Adapter (rev 01)
ad:00.1 Fibre Channel: QLogic Corp. ISP2722-based 16/32Gb Fibre Channel to PCIe Adapter (rev 01)

3.4 Configuring the hypervisor operating system #

 

The hypervisor host operating system needs to be configured to assure compatibility and maxized performance for an SAP HANA VM.

3.4.1 Installing vhostmd #

 

The hypervisor needs to have the vhostmd package installed and the corresponding vhostmd service enabled and started. This is described in SAP Note 1522993 - "Linux: SAP on SUSE KVM - Kernel-based Virtual Machine".

3.4.2 Tuning the generic host with tuned #

 

To apply some less specific, but nevertheless effective, tuning to the host, the TuneD tool (https://tuned-project.org/) can be used.

When installed (the package name is tuned), one of the preconfigured profiles can be selected, or a custom one created. Specifically, the virtual-host profile should be chosen. Do not use the sap-hana profile on the hypervisor. This can be achieved with the following commands:

zypper in tuned

systemctl enable tuned

systemctl start tuned

tuned-adm profile virtual-host

The tuned daemon should now start automatically at boot time, and it should always load the virtual-host profile, so there is no need to add any of the above commands in any custom start-up script. If in doubt, it is possible to check with the following command whether tuned is running and what the current profile is :

tuned-adm profile

Available profiles:
- balanced                    - General non-specialized tuned profile
...
- virtual-guest               - Optimize for running inside a virtual guest
- virtual-host                - Optimize for running KVM guests
Current active profile: virtual-host

3.4.2.1 Power management considerations #

 

The CPU frequency governor should be set to performance to avoid latency issues because of ramping the CPU frequency up and down in response to changes in the system’s load. The selected tuned profile should have done this already, and with the following command, it is possible to verify that it actually did:

cpupower -c all  frequency-info

The governor setting can be verified by looking at the current policy.

Additionally, the performance bias setting should also be set to 0 (performance). The performance bias setting can be verified with the following command:

cpupower -c all info

Modern processors also attempt to save power when they are idle, by switching to a lower power state. Unfortunately this incurs latency when switching in and out of these states.

To avoid that, and achieve better and more consistent the performance, the CPUs should not be allowed to go into too aggressive power saving modes (known as C-states). It therefore is recommended that only C0 and C1 are used.

This can be enforced by adding the following parameters to the kernel boot command line: intel_idle.max_cstate=1.

To double check that only the desired C-states are actually available, the following command can be used:

cpupower idle-info

The idle state settings can be verified by looking at the line containing`Available idle states:`.

3.4.3 irqbalance #

 

The irqbalance service should be disabled because it can cause latency issues when the /proc/irq/* files are read. To disable irqbalance run the following command:

systemctl disable irqbalance.service

systemctl stop irqbalance.service

3.4.4 Kernel Samepage Merging (ksm) #

 

Kernel Samepage Merging (KSM, https://www.kernel.org/doc/html/latest/admin-guide/mm/ksm.html ) is of no use, because there is only one single VM. Thus it should be disabled. The following command makes sure that it is tuned off and that any sharing and de-duplication activity that may have happened, in case it was enabled, is reverted:

echo 2 >  /sys/kernel/mm/ksm/run

3.4.5 Customizing the Linux kernel boot options #

 

To edit the boot options for the Linux kernel, perform the following steps:

1. Edit /etc/defaults/grub and add the following boot options to the line GRUB_CMDLINE_LINUX_DEFAULT (a detailed explanation of these options will follow).

   mitigations=auto kvm.nx_huge_pages=off numa_balancing=disable kvm_intel.ple_gap=0 transparent_hugepage=never intel_idle.max_cstate=1 default_hugepagesz=1GB hugepagesz=1GB hugepages=<number of hugepages> intel_iommu=on iommu=pt intremap=no_x2apic_optout

2. Run the following command:

   update-bootloader

3. Reboot the system:

   reboot

3.4.6 Technical explanation of the above described configuration settings #

 

Hardware vulnerabilities mitigations (mitigations=auto kvm.nx_huge_pages=off)

Recently, a class of side channel attacks exploiting the branch prediction and the speculative execution capabilities of modern CPUs appeared. On an affected CPU, these problems cannot be fixed, but their effect and their actual exploitability can be mitigated in software. However, this sometimes has a non-negligible impact on the performance.

For achieving the best possible security, the software mitigations for these vulnerabilities are being enabled (mitigations=auto) with the only exception of the one that deals with "Machine Check Error Avoidance on Page Size Change (CVE-2018-12207, also known as "iTLB Multiht").

Automatic NUMA balancing (numa_balancing=disable)

Automatic NUMA balancing can result in increased system latency and should therefore be disabled.

KVM PLE-GAP (kvm_intel.ple_gap=0)

Pause Loop Exit (PLE) is a feature whereby a spinning guest CPU releases the physical CPU until a lock is free. This is useful in cases where multiple virtual CPUs are using the same physical CPU but causes unnecessary delays when the system is not overcommitted.

Transparent huge pages (transparent_hugepage=never)

Because 1 GiB pages are used for the virtual machine, then there is no additional benefit from having THP enabled. Disabling it will avoid khugepaged interfering with the virtual machine while it scans for pages to promote to hugepages.

Processor C-states (intel_idle.max_cstate=1)

Optimal performance is achieved by limiting the processor to states C0 (normal running state) and C1 (first lower power state).

Note that, while there is an exit latency associated with C1 states, it is offset on hyperthread-enabled platforms by the fact sibling cores can borrow resources from sibling cores if they are in the C1 state and some CPUs can boost the CPU frequency higher if siblings are in the C1 state.

Huge pages (default_hugepagesz=1 GiB hugepagesz=<1 GiB hugepages=number of hugepages>)

The use of 1 GiB huge pages is to reduce overhead and contention when the guest is updating its page tables. This requires allocation of 1 GiB huge pages on the host. The number of pages to allocate depends on the memory size of the guest.

1 GiB pages are not pageable by the OS. Thus they always remain in RAM and therefore the locked definition in libvirt XML files is not required.

It also important to ensure the order of the huge page options. Specifically the <number of hugepages> option must be placed after the 1 GiB huge page size definitions.

Note: Calculating value

The value for <number of hugepages> should be calculated by taking the number GiB’s of RAM minus approx. 8% for the hypervisor OS. For example, 3 TiB RAM (3072 GiB) minus 8% are approximately 2770 huge pages.

PCI Passthrough (intel_iommu=on iommu=pt)

For being able to directly assign host devices (like storage controllers and NIC Virtual Functions), with PCI Passthrough and SR-IOV, the IOMMU must be enabled. On top of that, iommu=pt makes sure that you set up the devices for the best performance (that is, passthrough mode).

Interrupt remapping (intremap=no_x2apic_optout)

Interrupt remapping interrupts from devices to be intercepted, validated and routed to a specific CPU (for example, one where a virtual CPU of the guest VM that has the device assigned is running). This parameter makes sure that such feature is always enabled.

This section describes the modifications required to the libvirt XML definition of the guest VM. The libvirt XML may be edited using the following command:

virsh edit Guest VM name

4.3 Backing memory #

 

Huge pages, sized 1 GiB (that is, 1048576 KiB), must be used for all the guest VM memory. This guarantees optimal performance for the guest VM.

It is necessary that each NUMA cell of the guest VM have a whole number of huge pages assigned to them (that is, no fractions of huge pages). All the NUMA cells should also have the same number of huge pages assigned to them (that is, the guest VM memory configuration must be balanced).

Therefore the number of huge pages needs to be dividable by the number of NUMA cells.

For example, if the host has 3169956100 KiB (that is, 3 TiB) of memory and we want to leave 91.75% of it to the hypervisor (see Section 2.2.2, “Memory sizing”), and there are 4 NUMA cells, each NUMA cell will have the following number of huge pages:

• (3169956100 * (91.75/100)) / 1048576 / 4 = 693

This means that, in total, there will need to be the following number of huge pages:

• 693 * 4 = 2772

Such number must be passed to the host kernel command line parameter on boot (that is hugepages=2772, see Section 3.4.6, “Technical explanation of the above described configuration settings”).

Both the total amount of memory the guest VM should use and the fact that such memory must come from 1 GiB huge pages need to be specified in the guest VM configuration file.

It must also be ensured that the memory and the currentMemory element have the same value, to disable memory ballooning, which, if enabled, would cause unacceptable latency:

<domain type='kvm'>
  <!-- ... -->
  <memory unit='KiB'>2906652672</memory>
  <currentMemory unit='KiB'>2906652672</currentMemory>
  <memoryBacking>
    <hugepages>
      <page size='1048576' unit='KiB'/>
    </hugepages>
    <nosharepages/>
  </memoryBacking>
  <!-- ... -->
</domain>

Note: Memory Unit

The memory unit can be set to GiB to ease the memory computations.

<domain type='kvm'>
  <!-- ... -->
  <cpu mode='host-passthrough' check='none'>
    <topology sockets='4' cores='28' threads='2'/>
    <feature policy='require' name='rdtscp'/>
    <feature policy='require' name='invtsc'/>
    <feature policy='require' name='x2apic'/>
    <numa>
      <cell id='0' cpus='0-55' memory='726663168' unit='KiB'>
        <distances>
          <sibling id='0' value='10'/>
          <sibling id='1' value='21'/>
          <sibling id='2' value='21'/>
          <sibling id='3' value='21'/>
        </distances>
      </cell>
      <cell id='1' cpus='56-111' memory='726663168' unit='KiB'>
        <distances>
          <sibling id='0' value='21'/>
          <sibling id='1' value='10'/>
          <sibling id='2' value='21'/>
          <sibling id='3' value='21'/>
        </distances>
      </cell>
      <cell id='2' cpus='112-167' memory='726663168' unit='KiB'>
        <distances>
          <sibling id='0' value='21'/>
          <sibling id='1' value='21'/>
          <sibling id='2' value='10'/>
          <sibling id='3' value='21'/>
        </distances>
      </cell>
      <cell id='3' cpus='168-223' memory='726663168' unit='KiB'>
        <distances>
          <sibling id='0' value='21'/>
          <sibling id='1' value='21'/>
          <sibling id='2' value='21'/>
          <sibling id='3' value='10'/>
        </distances>
      </cell>
    </numa>
  </cpu>
  <!-- ... -->
</domain>

<domain type='kvm'>
  <vcpu placement='static'>224</vcpu>
  <cputune>
    <vcpupin vcpu='0' cpuset='0,112'/>
    <vcpupin vcpu='1' cpuset='0,112'/>
    <vcpupin vcpu='2' cpuset='1,113'/>
    <vcpupin vcpu='3' cpuset='1,113'/>
    <vcpupin vcpu='4' cpuset='2,114'/>
    <vcpupin vcpu='5' cpuset='2,114'/>
    <vcpupin vcpu='6' cpuset='3,115'/>
    <vcpupin vcpu='7' cpuset='3,115'/>
    <vcpupin vcpu='8' cpuset='4,116'/>
    <vcpupin vcpu='9' cpuset='4,116'/>
    <vcpupin vcpu='10' cpuset='5,117'/>
    <vcpupin vcpu='11' cpuset='5,117'/>
    <!-- output abbreviated -->
    <vcpupin vcpu='218' cpuset='109,221'/>
    <vcpupin vcpu='219' cpuset='109,221'/>
    <vcpupin vcpu='220' cpuset='110,222'/>
    <vcpupin vcpu='221' cpuset='110,222'/>
    <vcpupin vcpu='222' cpuset='111,223'/>
    <vcpupin vcpu='223' cpuset='111,223'/>
  </cputune>
  <numatune>
    <memory mode='strict' nodeset='0-3'/>
    <memnode cellid='0' mode='strict' nodeset='0'/>
    <memnode cellid='1' mode='strict' nodeset='1'/>
    <memnode cellid='2' mode='strict' nodeset='2'/>
    <memnode cellid='3' mode='strict' nodeset='3'/>
  </numatune>
  <!-- ... -->
</domain>

#!/usr/bin/env bash
NUM_VCPU=$(ls -d /sys/devices/system/cpu/cpu[0-9]* | wc -l)
echo "  <vcpu placement='static'>${NUM_VCPU}</vcpu>"
echo "  <cputune>"
THREAD_PAIRS="$(cat /sys/devices/system/cpu/cpu*/topology/core_cpus_list | sort -n | uniq )"
VCPU=0
for THREAD_PAIR in ${THREAD_PAIRS}; do
  for i in 1 2; do
    echo "    <vcpupin vcpu='${VCPU}' cpuset='${THREAD_PAIR}'/>"
    VCPU=$(( VCPU + 1 ))
  done
done
echo "  </cputune>"

lscpu --extended=CPU,SOCKET,CORE

lstopo-no-graphics

 <domain type='kvm'>
  <!-- ... -->
  <devices>
    <!-- ... -->
    <interface type='hostdev' managed='yes'>
      <mac address='52:54:00:7f:12:fb'/>
      <driver name='vfio'/>
      <source>
        <address type='pci' domain='0x0000' bus='0x17' slot='0x02' function='0x0'/>
      </source>
    </interface>
    <!-- ... -->
  </devices>
  <!-- ... -->
</domain>

<domain type='kvm'>
  <!-- ... -->
  <devices>
    <!-- ... -->
    <disk type='block' device='disk'>
      <driver name='qemu' type='raw' cache='none' io='native'/>
      <source dev='/dev/disk/by-id/wwn-0x600000e00d29000000293db000520000'/>
      <target dev='vda' bus='virtio'/>
    </disk>
    <!-- ... -->
  </devices>
  <!-- ... -->
</domain>

<domain type='kvm'>
  <!-- ... -->
  <devices>
    <!-- ... -->
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <source>
        <address domain='0x0000' bus='0x85' slot='0x00' function='0x0'/>
      </source>
    </hostdev>
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <source>
        <address domain='0x0000' bus='0x85' slot='0x00' function='0x1'/>
      </source>
    </hostdev>
    <!-- ... -->
  </devices>
  <!-- ... -->
</domain>

<domain type='kvm'>
  <!-- ... -->
  <clock offset='utc'>
    <timer name='rtc' tickpolicy='catchup'/>
    <timer name='pit' tickpolicy='delay'/>
    <timer name='hpet' present='no'/>
  </clock>
  <!-- ... -->
</domain>

 <domain type='kvm'>
  <!-- ... -->
  <devices>
    <!-- ... -->
    <rng model='virtio'>
      <backend model='random'>/dev/urandom</backend>
    </rng>
    <!-- ... -->
  </devices>
  <!-- ... -->
</domain>

<domain type='kvm'>
  <!-- ... -->
  <features>
    <!-- ... -->
    <kvm>
      <hint-dedicated state='on'/>
    </kvm>
  </features>
  <!-- ... -->
</domain>

The Linux kernel has code to mitigate existing vulnerabilities of the 1st Generation Intel Xeon Scalable Processor (Skylake) CPUs. Our testing showed no visible impact of those mitigations with regard to SAP HANA performance, except for the iTLB Multihit mitigation. This mitigation can be controlled by the kernel parameter kvm.nx_huge_pages (see SUSE support document 7023735).

In general, the setting of parameter kvm.nx_huge_pages has an impact on performance. The implications on performance need to be considered as laid out in the Skylake example below.

Performance deviations for virtualization as measured on Intel Skylake (Bare Metal to single VM):

For a full explanation of administration commands, refer to official SUSE Virtualization documentation such as:

cat /proc/cmdline

cat /proc/meminfo | grep Huge

virsh list --all

virsh start VM/Guest Domain name

virsh shutdown VM/Guest Domain name

/etc/libvirt/qemu

/var/log/libvirt/qemu

lscpu | grep L3

lscpu

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Copyright (c) YEAR YOUR NAME.
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