Managing Logical Processors on the IBM eserver zseries z990

Transcription

1 Managing Logical Processors on the IBM eserver zseries z990 The z990 is the first zseries processor to implement a multibook architecture. This article provides some suggestions on logical CP assignment which may help to optimize the capacity of a z990 as a result of this multibook implementation. Each book of a z990 contains up to 8 user definable CPs, a level 1 cache for each CP and a level 2 cache as well as memory. A single book CEC is called an A08, a two book CEC is called a B16, a three book CEC is called a C24 and a four book CEC is called a D32. Changes have been made to the PR/SM TM hipervisor to optimize the capacity of this environment. Complete details of these changes can be found in the IBM Research and Development article titled Logical Partition Mode Physical Resource Management on the IBM eserver z990 at the following URL: An understanding of the z990 s multibook architecture and the method in which logical CPs are assigned to a partition has led to a new recommendation on assigning logical CPs to a partition. The reasons for these changes are outlined below. Optimizing Primary Book Assignments on a z990 In a partition environment the user must assign the number of logical CPs to each LPAR. Using this information the hipervisor will assign logical CPs to physical CPs of a home book. Ideally, all of the logical CPU affinities for a logical partition are established on the same book. There are several different goals of varying importance the hipervisor considers when evaluating potential solutions. The following goals are applied to the allocation of resources, listed from highest to lowest priority: 1. Logical CPUs should be distributed as evenly as possible across the available physical CPUs so the maximum utilization of physical CPUs is achieved. 2. Logical CPUs with the same logical partition should be concentrated on the smallest number of books possible in order to minimize cross-book cache interrogation overhead. 3. The degree to which the logical CPUs and memory of the logical partition are on the same book should be maximized. 4. A best-fit solution is preferred to a most available solution. A best-fit solution is one with the smallest amount of resource in excess of what is required. For example a single partition needs 2 Gbytes of memory. There are two books with available memory, the first book has 3 Gbytes of available memory while the Managing Logical Processors on the z990 Page 1

2 second book has 10 Gbytes of available memory. The first book is selected as the best fit solution. A solution with the greatest amount of resource in excess of what is required is said to be the most available solution. Consistent choice of a best-fit solution over a most available solution provides the greatest likelihood subsequent requests will find enough resource available. For each logical partition, each potential solution is identified and evaluated with respect to the degree to which it satisfies all of the goals at partition activation time. The most highly valued solution is then implemented. Logical CPUs to which physical CPUs are dedicated have a hard affinity for those CPUs because they are always dispatched on only the physical CPUs dedicated to them. Shared logical CPUs have a soft affinity for the nondedicated physical CPUs on whatever book has been chosen. If they cannot be dispatched on those physical CPUs at any particular time, others in the system on a nonpreferred book are considered. Reoptimizing primary book assignments on the z990 system Once established, physical CPU affinity for a dedicated logical CPU cannot change because the hipervisor does not have the ability to rededicate a different physical CPU transparent to the logical partition. Shared logical CPU affinities determined to be optimal at logical partition activation may require reevaluation when the availability and usage of system resources change. Since the distribution of logical CPU weights among other logical partitions can affect the optimum affinity for any particular logical partition, an occurrence necessitating reoptimization generally affects all currently active logical partitions using shared logical CPUs. The following events require reoptimization: 1. Configure ON of additional physical CPUs, as for concurrent capacity backup (CBU). 2. Configure OFF of physical CPUs, as for concurrent CBU undo. 3. Dedication of a physical CPU to a logical CPU if the dedication reduces the number of shared physical CPUs remaining on the book below the maximum number of logical CPUs with affinity to that book. The reoptimization is done for any logical partition with shared logical CPUs. 4. Checkstop of a physical CPU when no spare is available on the system. 5. Transparent sparing of a checkstopped physical CPU when the CPU brought into the configuration comes from a book different from the one containing the broken CPU. 6. Logical partition activation of shared logical partitions so the distribution of shared weights can be equalized among all of the books. 7. Configure ON of a shared logical CPU. Reoptimization is limited to the logical CPUs of the initiating logical partition to avoid excessive churning of remaining logical partitions. Managing Logical Processors on the z990 Page 2

3 User Influence on the Hipervisor Optimization The PR/SM TM hipervisor optimization shields the user from being concerned with the placement of logical CPs in specific books. Installations, and the methods they use to activate partitions, may influence the results of this optimization. Increased care in the method of partition activation may help insure an optimal solution. This document will describe new recommendations for defining shared logical CPs to provide better input to the hipervisor optimization process. Let s review the method to define logical CPs to a partition. Using the LPAR Activation Panel on the HMC the user defines both an INITIAL and RESERVED number of logical CPs. The INITIAL field identifies the number of logical CPs available to the partition. This value is used in the hipervisor optimization process. This value can range from a minimum of 1 to a maximum of the number of purchased processors. The RESERVED field identifies the potential number of logical CPs which can be added to a partition after activation. Users wishing to bring on an available reserved CP would use the MVS CF online command. This value can range from 0 to the total number of potential processors minus the value specified in the initial field. The screen below is a sample of the HMC panel showing the INITIAL and RESERVED fields. Your screen may differ depending on the machine model and microcode level. Managing Logical Processors on the z990 Page 3

4 This document will discuss a common technique used when activating partitions. The document will offer recommendations on alternative approaches for partition activation. Recommendations for both IRD and non-ird environments will be offered. Activation Method for Maximum Flexibility A popular technique is allowing a partition to have access to all of the physical CPs in a CEC and then using automation or operator commands to configure off logical CPs to a number more in line with the capacity requirements. IRD will also follow this approach, bringing all logical CPs online as defined by the INITIAL value. IRD will then vary off excess CPs to match the resource requirements. With an increased understanding of the partition optimization process a better approach is to set the INITIAL field equal to the number of CPs required to support the peak capacity. Additional installed CPs defined in the RESERVED field can still be added dynamically to the partition using the MVS CF command. As an example, assume a is defined using a four book configuration. This processor, because of the 4 book configuration, could eventually be upgraded to a Managing Logical Processors on the z990 Page 4

5 maximum of 32 CPs. For this example assume the processor will support two partitions and each requires 50% of the currently installed 16 CPs. Current configuration technique: With the configuration described above the following details the operational process used to activate and IPL the partitions in the current procedure. 1. Define each partition with an INITIAL CP value of 16 and a RESERVED value of Activate each partition 3. The partitions after IPL will have 16 logical CPs online. Operations will then configure off 6 logical CPs to create a partition with 10 logical CPs online. Eight are required to support the 50% requirement, while the additional 2 are online to support any spike in CP demand. 4. Configure online the currently installed 6 logical CPs if needed 5. Sixteen additional CPs could be configured online to the partition if they were physically enabled. Recommended configuration technique: Because of the multi-book configuration, and with knowledge of the partition optimization, a better method of activating the environment is described below. 1. Define each partition with an INITIAL CP value of 10 and a RESERVED value of Activate each partition 3. The partition after IPL will have 10 logical CPs online. Eight are required to support the 50% requirement, while the additional 2 are online to support a spike in CP demand. 4. Six additional CPs could be configured online if an abnormal situation required the additional capacity while an additional 16 could be configured online if they were physically enabled. This technique should be used when defining general purpose CPs and zaaps. On the HMC zaaps are called IFAs. The major difference in these techniques is you want the initial definition to more closely match the actual configuration. IRD Recommendations IRD Vary CPU Management provides the capability to allow WLM to configure CPs online and offline to a partition to meet the CPU capacity requirements. IRD will manage the number of online CPs defined in the INITIAL field, as well as any CPs which have been manually configured online by the operator. Existing IRD documentation suggests IRD users place all available CPs into the INITIAL field. This would have the benefit of giving the most control to IRD to manage CPs. These recommendations were made concurrent with the introduction of the z900. The Managing Logical Processors on the z990 Page 5

6 z990 is the first multi-book processors and as a result of the optimization done at partition activation a change in the previous recommendations is warranted. IRD users are urged to make the INITIAL values equal to the number of online logical CPs required to meet peak processor demand. This will allow the hipervisor to get a better view of the true resource requirements and aid the optimization in reaching a preferred solution. Conclusions The hipervisor provides a sophisticated set of algorithms to optimize the placement of logical CPs into the appropriate books. These new recommendations have the potential to help with this optimization as the INITIAL CP configuration will more closely match the number of processors being used versus an artificially high value used only until the IPL process is complete. Artificially high values could result in configurations which are not ideal. Simple changes in partition activation management will provide a clearer view of required resources resulting in more optimal logical CP assignments. These recommendations are made for the IBM eserver zseries z990 processor only. The hipervisor optimization process has been enhanced on the System z9 and should not require adherence to this recommendation. Special Notices: The information contained in this document has not been submitted to any formal IBM test and is distributed on as as is basis without any warranty either expressed or implied. The use of this information or the implementation of any of these techniques is a customer responsibility and depends on the customer s ability to evaluate and integrate them into the customer s operational environment. While each item may have been reviewed by IBM for accuracy in a specific situation, there is no guarantee the same or similar results will be obtained elsewhere. Customers attempting to adapt these techniques to their environment do so at their own risk. Performance data contained in this document was determined in a controlled environment with no other processing occurring and do not represent actual field measurement; therefore, the results which may be obtained in other operating environments may vary significantly. No commitment as to your ability to obtain comparable results is in any way intended or made by this release of information. Managing Logical Processors on the z990 Page 6