CPU Configuration Guidelines for vPars

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White paper

Audience..................................................................................................................................... 2

HP-UX Virtual Partitions Overview................................................................................................... 2

2.1

CPU Assignment on vPars Releases Prior to A.04.01 ................................................................. 2

2.2

CPU Assignment on vPars Releases Starting with A.04.01 ......................................................... 2

2.3

Count and Path Based Assignment of CPU’s ............................................................................. 3

Establishing a Baseline Configuration ............................................................................................. 6

3.1

Determining Minimum CPU Configuration ................................................................................ 6

3.2

Determining Maximum CPU Configuration ............................................................................... 9

3.3

CPU Configuration Results.................................................................................................... 11

Configuring the CPU’s on vPars.................................................................................................... 12

4.1

I/O Interrupt Assignment on HP-UX ....................................................................................... 12

4.2

CPU Configuration on A.04.01 ............................................................................................ 12

4.3

Count Based CPU Migration................................................................................................. 17

Flexing Dynamic CPU Migration on A.04.01................................................................................. 18

5.1

Manual Redistribution of I/O Interrupts .................................................................................. 19

5.2

Interrupt Save and Restore.................................................................................................... 21

Summary................................................................................................................................... 25

Additional Considerations ........................................................................................................... 26

For more information .................................................................................................................. 27

Summary of content (27 pages)

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CPU Configuration Guidelines for vPars White paper 1 Audience..................................................................................................................................... 2 2 HP-UX Virtual Partitions Overview................................................................................................... 2 2.1 CPU Assignment on vPars Releases Prior to A.04.01 ................................................................. 2 2.
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1 Audience This white paper is intended for individuals who are interested in using HP-UX virtual partitions (vPars) to consolidate multiple systems onto a single system or hard partition. This document explains how to manage CPU assignments on vPars to achieve predictable performance under varying workloads. This paper assumes that the reader has a good knowledge of the HP-UX operating system and is familiar with the concepts of vPars, processor sets, and I/O interrupts processing.
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row containing the name of the vPar with the value under the Num CPU’s column. This value is the current number of CPU’s that the vPar owns and it is maintained across OS boots. The following are definitions of configuration parameters for vPar CPU’s. • min – user configurable setting for the minimum number of CPU’s that are assigned to a vPar. • max – user configurable setting for the maximum number of CPU’s that are assigned to a vPar.
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Figure 2. CPU configuration for vpolyc01 after addition of 2 CPU’s. Figure 3. CPU configuration for vpolyc01 showing 3 count based CPU’s.
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Figure 4. Display of CPU’s in the available pool. Figure 5. Addition of CPU’s 0.121 and 0.122 to vpolyc01. Note that specifying the 2 CPU’s by path has placed them in the user assigned category.
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3 Establishing a Baseline Configuration The key to achieving consistent system performance is matching the system resources (CPU, memory, and I/O) to its dynamic workloads. Over configuring a system is one way of achieving this goal but it comes at the cost of under-utilized resources when peak workloads are absent. One method of utilizing CPU’s more effectively is to migrate them to where the workload on the system requires them.
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partition is available to the application. The variable factor in this experiment will be the CPU’s available to execute the workload. The creation of the real time processor set is shown in Figure 6. Before beginning the test, “top” is started and the file system and disk stress workloads are applied to the 8 CPU system. When the workload has reached a steady state, determine the CPU utilization by subtracting the CPU IDLE from 100%.
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Figure 7. Steady state workload applied to all 8 CPU’s. Figure 8. Move 2 CPU’s from the default processor set to the real time processor set. Figure 9. CPU utilization with 6 CPU’s.
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Figure 10. The CPU utilization objective is achieved with 4 CPU’s. 3.2 Determining Maximum CPU Configuration The objective of this section is to experimentally determine the maximum number of CPU’s that a specific workload will need in order to satisfy a 60% increase in workload from the steady state run made in the previous section. With top running, increase the file system and disk stress workload by approximately 60% and observe the CPU utilization of the system.
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Figure 12. Move a CPU from the real time processor set to the default processor set and rerun the workload. Figure 13. The addition of one CPU has increased the CPU utilization rate close to the target value. Figure 14. The addition of one more CPU has brought the CPU utilization to its stated objective.
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3.3 CPU Configuration Results In order to meet the objective of 60% CPU utilization for steady state and peak workloads, a CPU configuration consisting of 4 CPU’s for the minimum and 6 CPU’s for the maximum are needed. These CPU parameters will be used to configure a vPar in the next section.
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4 Configuring the CPU’s on vPars In the previous section it was determined experimentally that 4 CPU’s are required to sustain the steady state workload and meet the 60% CPU utilization objective. The experiment also determined that 6 CPU’s are required to sustain the peak workload and meet the 60% CPU utilization objective. Now that the CPU configuration to meet these performance objectives is known, it should be a simple matter to configure the CPU’s for the vPar.
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count based semantics when migrating CPU’s. The following paragraph will explain how to create a vPar with path based CPU assignments. Before creating the vPar, execute the vparstatus command to view the defined partitions and the resources allocated to them (Figure 15). Now execute the vparstatus –A command to view the resources available to create the vPar. Figure 16 shows the command syntax and the output from the vparstatus –A command.
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Figure 16. The available resources that can be assigned to the partition named vpolyc01. Figure 17. The creation of the partition plan for vpolyc01 and the addition of the 4 path based CPU’s and the adjustment of the minimum number of CPU’s.
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Figure 18. The results of adding the 4 user assigned CPU’s to vpolyc01.
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Figure 19. The partition plan for vpolyc01 is completed with the addition of memory and I/O devices.
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Figure 20. Interrupt assignments as viewed from the output of the intctl command. 4.3 Count Based CPU Migration When the workload on vpolyc01 increases, one or more CPU’s can be added to process the additional load. The following vparmodify example shows the syntax that should be used to add the count based CPU’s. vparmodify –p vpolyc01 –a cpu::2 As mentioned earlier, adding CPU’s does not change the interrupt assignment so all interrupts are still assigned to the four original CPU’s.
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5 Flexing Dynamic CPU Migration on A.04.01 In section 4.2, the CPU configuration for the vPar vpolyc01 was created as a way to simulate the behavior of bound and unbound CPU’s of vPars versions prior to A.04.01. The path based CPU assignments represent the bound CPU’s and the count based CPU assignments represent the unbound CPU’s. Configuring CPU’s by this method allows I/O interrupt processing to execute on a fixed set of CPU’s.
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Figure 22. GlancePlus individual CPU utilization report. 5.1 Manual Redistribution of I/O Interrupts There are two ways of redistributing the I/O interrupts across CPU’s: reboot the vPar that requires the I/O interrupts to be redistributed or use the intctl command to move interrupts from over-utilized CPU’s to under-utilized CPU’s. The first option requires downtime and is normally not an option. The second choice requires rolling up your sleeves and figuring out how to distribute the I/O interrupts.
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Figure 24 shows the assignment of interrupts after moving 7 CPU’s to the real time processor set and back again. The net effect is that all I/O interrupts were migrated to the boot CPU and I/O interrupt processing has become burdensome for this CPU. Figure 25 shows the sequence of intctl commands used to redistribute interrupts over 4 of the 8 CPU’s present. Figure 23. Output of intctl show I/O interrupts distributed across 4 CPU’s. Figure 24.
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Figure 25. Sequence of intctl commands to redistribute I/O interrupts. 5.2 Interrupt Save and Restore The intctl command has a –s or save option to allow the system administrator to snapshot the current I/O interrupt assignments and save them to a file. This allows the default interrupt assignments created during boot by the HP-UX kernel to be overridden for better balance.
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Figure 26 shows the output of the intctl –p command which has an additional field that maps the CPU ID to the CPU hardware path. This mapping is important for assigning path based CPU’s and for migrating I/O interrupts. Figure 27 shows the current interrupt assignments stored in the file named ints after issuing the intctl –s command. This file can be used as input to the intctl –r command to restore the I/O interrupt assignment after CPU migrations have taken place.
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Figure 27. Display of I/O interrupt assignments saved to the file named ints by the intctl –s command. Figure 28. Interrupt assignments after 6 CPU’s move to real-time processor set.
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Figure 29. Interrupt assignment after 6 CPU’s move from real-time processor set to default processor set and Interrupt restoration.
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6 Summary A workload must be characterized in order to configure a system for consistent performance. Choose a metric to optimize for (response time, throughput, or utilization) and specify a configuration with enough memory and I/O to sustain the peak workload. Use the method presented in this paper to establish the minimum and maximum CPU configuration parameters. For vPars version prior to A.04.01, the bound to unbound CPU ratio can be determined by using the method detailed in section 3.
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7 Additional Considerations The WLM product literature warns against using path based assignments. Compatibility of WLM’s virtual partition management and certain CPU bindings Do not use cell-specific CPU bindings or user-assigned CPU bindings on virtual partitions you are going to manage with WLM. If using WLM do not use path based CPU assignments (path based is another name for userassigned).
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8 For more information http://www.hp.com/go/virtualization (HP-UX Virtualization) http://docs.hp.com/en/5969-4363/index.html (HP-UX Interrupt Migration Product Note) http://docs.hp.com/en/5185-4322/5185-4322.pdf (HP-UX Processor Sets White Paper) http://docs.hp.com/en/B2355-60103/psrset.1M.html (HP-UX Processor Sets Manual Pages) http://www.hp.com/go/wlm (HP-UX Workload Manager) © 2005 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice.