Method and system for managing resource allocation in non-uniform resource access computer systems

A method and system of managing resource allocation in a non-uniform resource access computer system is disclosed. A method comprises determining access costs between resources in a computer system having non-uniform access costs between the resources. The method also includes constructing a hierarchical data structure comprising the access costs. The hierarchical data structure is traversed to manage a set of the resources.

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

The present invention relates to the field of non-uniform resource access computer systems. Specifically, embodiments of the present invention relate to methods and systems providing a hierarchical data structure describing access costs to resources in order to facilitate managing the resources.

BACKGROUND ART

Uniform Memory Access (UMA) computer systems have the characteristic of a processor, for example, CPU (Central Processing Unit), having essentially the same access time to all memory resources. There may be multiple CPUs in such a system, each with the characteristic of little or no performance difference for one memory resource over another based on access cost. In such a system, there is little or no benefit in assigning memory resources to a given CPU based on expected access time. In contrast, for Non-Uniform Memory Access (NUMA) computer systems, the cost for a CPU to access memory can vary significantly for different memory resources. For example, some memory resources may be closer to a CPU and others farther away. Thus, there can be a benefit of assigning a CPU or memory resource to a process based on expected access cost.

One conventional technique of allocating CPU and memory resources based on access time is to discover details of the hardware configuration to determine which memory resources are near which CPUs. However, the hardware configuration information that is typically collected does not easily facilitate the allocation of resources. For example, the hardware configuration information may include details about CPUs, physical addresses, boards, etc. It is difficult to base a resource allocation decision based on such hardware configuration information. Further, while the hardware configuration information can be passed to an application program, the application program must understand how the operating system and hardware function in order to take advantage of the hardware configuration information. Moreover, modifying the application program to take advantage of the hardware configuration information makes the application program less portable.

To avoid the above complications, CPU and memory resources can be allocated without regard to access cost. While this technique is simple, it results in slower execution than would be possible with a more intelligent allocation of CPU and memory resources. While the above discusses problems with allocating CPU and memory resources, allocating resources other than CPU and memory resources also presents problems for conventional techniques.

Therefore, a problem with conventional methods of allocating resources in non-uniform resource access computer systems is the difficulty in basing a resource allocation decision on hardware configuration information. Another problem with conventional methods of allocating resources in non-uniform resource access computer systems is that application programs need to be modified to allow them to take advantage of hardware configuration information. Another problem is the inefficient allocation of resources when resources are allocated without regard to access costs.

SUMMARY OF THE INVENTION

The present invention provides methods and systems of facilitating resource management in a non-uniform resource access computer system. Embodiments of the present invention allow a resource allocator to easily decide between a resource with the lowest access cost, a next lowest access cost, etc. Embodiments of the present invention may be transparent to application programs, and hence do not require modification to the application programs. However, embodiments of the present invention may also provide access cost information to applications to allow observability and the opportunity to use the information to customize its resource allocation as it pleases. Embodiments of the present invention facilitate efficient allocation of resources in a non-uniform resource access computer system. The present invention provides these advantages and others not specifically mentioned above but described in the sections to follow.

Embodiments of the present invention provide an abstraction for the operating system and application programs to use for improving performance on NUMA machines. An access cost group is used to represent a group of resources that share a common access cost value. For example, an access cost group may contain a group of CPUs and a memory resource, wherein each of the CPUs has the same access cost value to the memory resource, or vice versa. An access cost function defines how the access cost value is calculated and may be defined by any suitable combination of parameters. Access cost groups are arranged in a hierarchical data structure such that children contain resources that are closer together than the resources contained in the child's parent(s). The hierarchical data structure makes it easy for the operating system and application programs to determine what resources are close to each other without knowing the details of the hardware. The hierarchical data structure makes it possible to determine not only the closest resource, but also the next closest resource and each successive closest resource.

Methods and systems of managing resource allocation in a non-uniform resource access computer system are disclosed. A method comprises determining access costs between resources in a computer system having non-uniform access costs between the resources. The method also includes constructing a hierarchical data structure comprising the access costs. The hierarchical data structure is traversed to manage a set of the resources.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the present invention, methods and systems of facilitating resource management in a non-uniform resource access computer system, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be recognized by one skilled in the art that the present invention may be practiced without these specific details or with equivalents thereof. In other instances, well-known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the present invention.

Notation and Nomenclature

It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussions, it is appreciated that throughout the present invention, discussions utilizing terms such as “traversing” or “processing” or “computing” or “forming” or “calculating” or “determining” or “allocating” or “recognizing” or “generating” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.

Managing Resource Allocation

Embodiments of the present invention provide a method and system of managing resource allocation in a non-uniform resource access computer system. For example, embodiments facilitate allocating memory to a process running in a CPU in a Non-Uniform Memory Access (NUMA) system. However, the present invention is not limited to the resources being CPUs and memory resources. For example, the resources may be input/output devices. Embodiments of the present invention abstract away from hardware configuration information such that the resource allocator does not need to know the details of the hardware configuration.

FIG. 1Aillustrates an exemplary hierarchical data structure120that facilitates managing resources in a computer system having non-uniform access between resources, according to an embodiment of the present invention. Typically, the hierarchical data structure120is constructed by an operating system, although this is not a requirement. The hierarchical data structure120is usually constructed when the computer system is booted. However, changes can be made to the hierarchical data structure120at any time, and it can be constructed at any time. The hierarchical data structure120can be used by an operating system, an application program, etc., to facilitate resource allocation. However, it is not required that an application program use or even be aware of the hierarchical data structure120when requesting resources. Therefore, no modifications have to be made to application programs to take advantage of the improved efficiency available through embodiments of the present invention.

The exemplary hierarchical data structure120ofFIG. 1Acontains access cost information such that resources can be conveniently allocated without the resource allocator or requester knowing anything more about the hardware configuration. The access cost is generally not an inherent cost of accessing the resource, but is instead the cost of accessing the resource from some point. For example, the access cost may be the cost for a CPU to access a memory resource. More generally, the access cost is the cost for resource A to access resource B. Thus, in the previous example, the term “resource” is applied to both the CPU and the memory. In some cases, the access cost from resource A to resource B is the same in each direction, and this may be reflected in the construction of the hierarchical data structure120. In other cases, the access cost from resource A to resource B does not equal the access cost in the other direction, and this would be reflected in the construction of the hierarchical data structure120. The access costs are ordered in the exemplary hierarchical data structure120such that the exemplary hierarchical data structure120can be traversed to determine resources having a series of alternative access costs ranging from a best alternative, to a next best alternative, etc.

FIG. 1Billustrates an exemplary non-uniform resource access computer system150having a ring topology, which will be used to explain principles of embodiments of the present invention. However, the present invention is not limited to ring topologies. The exemplary computer system150comprises CPUs152and memory resources155. However, the present invention is applicable for resources other than CPUs152and memory resources155. For example, the resources may be input/output devices. The exemplary computer system150comprises three local groups145A-C, each of which is depicted with CPUs152a-nand a single memory resource155. A single memory resource155is shown to illustrate that, within a local group145, the access cost between a CPU152and a memory resource155is essentially the same for any memory resource155within the local group145. Local groups145are not a required element of the present invention.

Still referring toFIG. 1B, the access cost may be measured in terms of latency, although other measures may be used, alone or in combination. Typically, a CPU152will be allocated a memory resource155within its local group145, as that has the lowest latency. However, it may become necessary, or at least desirable, for a CPU152to access a memory resource155outside of its local group145. In this case, the latency will typically increase, and perhaps by a considerable amount. Moreover, the latency for a CPU152to access a memory resource155outside of its local group145is non-uniform. For example, the latency may be two units for a CPU152in group145A to access a memory resource155in group145, while the latency may be four units for a CPU152in group145A to access a memory resource155in group145C.

Referring now to bothFIGS. 1A and 1B, the embodiment ofFIG. 1Aillustrates an exemplary hierarchical data structure120having four-levels. In this embodiment, the levels relate to how many hops there are between a CPU152and a memory resource155. For example, the first level contains access costs for various cases in which a CPU152and a memory resource155are in the same local group145. Note that there are many CPUs in a given local group145. The nodes at the second level contain access costs for various cases in which there is a single hop in the ring topology between a CPU152and a memory resource155. The nodes at the third level contain access costs for various cases in which there are two hops in the ring topology between a CPU152and a memory resource155. However, the hierarchical data structure does not have to be organized in levels corresponding to hops in the ring topology. For example, the hierarchical data structure120may contain fewer levels as a simplification if less detail were sufficient or desired.

An access cost is indicated in parenthesis in each node of the exemplary hierarchical data structure120and, in general, access costs rise when proceeding from leaves to the root of the exemplary hierarchical data structure120. Each node of the exemplary hierarchical data structure120corresponds to an access cost group. An access cost group defines the access cost between two or more resources in the exemplary system150. For example, an access cost may define the latency for a CPU152to access a memory resource155or the minimum latency for CPUs152a-nto access a memory resource155.

The nodes at the lowest level of the exemplary hierarchical data structure120correspond to the local groups145A-C in the exemplary system150and will be referred to as latency groups165a-c. For example, latency group165A in the exemplary hierarchical data structure120corresponds to local group145A the exemplary system150. There is not an access cost listed with this node because it is assumed that the local group will provide the lowest access cost, and thus the information is not needed for a resource allocation determination. However, there is no reason why an access cost cannot be listed in the nodes at the lowest level in the exemplary hierarchical data structure120. Moreover, the lowest level in the hierarchical data structure120does not have to be a local group145. As discussed earlier, the local group145is normally the best alternative in terms of access costs, but may not be available or desirable. As such, an alternative resource with a higher access cost may be allocated instead. Alternative resources are found by traversing upward in the exemplary hierarchical data structure120. Furthermore, the hierarchical data structure may be organized such that the resource with the next best access cost can be found in the parent of the current latency group.

With the exception of the root node, each of the latency groups165has at least one parent node, which defines a latency group165with an alternative access cost that is typically a higher access cost than its child node. Referring to the exemplary hierarchical data structure120, latency group165A has two parent nodes—the latency groups165A and165AC. Latency group165A reflects the cost for a CPU152in local group145A to access a memory resource155in local group145. The latency value in this case is two units. In one embodiment, the latency is defined by the lowest common latency experienced by any of the CPUs in local group145A. However, the present invention is not limited to this measure. Due to the symmetry of the exemplary computer system150, latency group165B also has latency group165AB as one of its parent nodes. Thus, latency group165AB also reflects the latency for a CPU152in local group145B to access a memory resource155in local group145A.

Latency group165AC reflects the cost for a CPU152in local group145A to access a memory resource155in local group145C. Latency group165AC also reflects the cost for a CPU152in local group145C to access a memory resource155in local group145A. Thus, in this embodiment, the latency groups165at the second level of the exemplary hierarchical data structure120represents access costs for cases in which there is a single hop in the ring topology. However, it is not required that each level in the exemplary hierarchical data structure120corresponds to a certain number of hops. Finishing off the second level of the exemplary hierarchical data structure120, latency group165BC reflects the cost for a CPU152in local group145B to access a memory resource155in local group145C and also the cost for a CPU152in local group145C to access a memory resource155in local group145B.

In some cases, the memory resource155is reached after two hops in the ring topology. The latency groups (165ACB,165BAC,165ABC) at the third level of the exemplary hierarchical data structure120represent cases in which the resource is reached in two hops of the ring topology. For latency group165ABC, the two hops are from local group145A to local group145B, and then to local group145C. Latency group165ABC has an access cost of five units, which is the sum of the access costs of the two hops. Group165ABC can also represent the access cost of a memory resource155in local group145A to a CPU152in local group145C via local group145B. Latency group165ACB represents the case of two hops between local group145A and local group145B via local group145C, and the reverse direction. Latency group165BAC represents the case of two hops between local group145B and local group145C via local group145A, and the reverse direction.

FIG. 2illustrates a process200of facilitating resource allocation in a computer system having non-uniform access between the resources, according to an embodiment of the present invention. Steps of process200may be stored in a computer readable medium and executed in a general-purpose processor. In step210, access costs are determined between resources in a computer system having non-uniform access costs between the resources. The manner of determining the access costs is not critical. In one embodiment, the access cost is measured in latency. Access cost may be defined by a function that comprises multiple parameters. The determination of access cost may involve determining latencies via a number of alternative paths between the resources. For example, inFIG. 1A, resources in local group145C may be accessed directly from local group145A or via a path through local group145B. Step210may comprise forming access cost groups that comprise groups of resources that share a common access cost. In one embodiment, step210comprises forming access cost groups that define an access cost between pairs of resources. For example, a given CPU and memory resource may form one pair. There may be many such pairs in a single access cost group.

In step220, a hierarchical data structure is formed comprising the access costs. The hierarchical structure is constructed to facilitate finding a resource near a selected resource, in terms of access cost. In one embodiment, a hierarchical data structure similar to the one illustrated inFIG. 1Ais constructed. However, the present invention is not so limited. For example, the exemplary hierarchical data structure ofFIG. 1Acomprises a number of latency groups165, such as latency group165A, which defines an access cost of two units between resources in local groups145A and145B. In one embodiment, step220comprises ordering the access groups into levels and forming the hierarchical data structure according to the levels.

In step230, the hierarchical data structure is traversed to determine a resource near a selected resource, in terms of the access costs. The near resource is not necessarily the nearest resource in terms of access costs.

In optional step240, a resource is allocated based on bandwidth considerations. For example, the access cost may be specified as a latency under conditions with no other traffic. An operating system may select a resource other than the one with the lowest access cost in order to spread traffic on the various datapaths.

FIG. 3illustrates a process300of traversing a hierarchical data structure to allocate resources, according to an embodiment of the present invention. Steps of process300may be stored in a computer readable medium and executed in a general-purpose processor. Process300ofFIG. 3will be discussed in conjunction withFIGS. 1A and 1B. For the purposes of explanation, process300will be described in connection with an exemplary resource allocation in which an operating system is allocating resources for a thread that has been assigned to local group145A inFIG. 1B. For example, the operating system may be allocating a memory resource given the CPU in which the thread is running. Alternatively, the operating system may be allocating a CPU based on a memory resource already assigned to the thread. The resource being allocated may be an input/output device instead of a CPU or memory. In step310, a set of latency groups are assigned to a given thread. This set will be referred to as the current set of latency groups.

In step315, the operating system attempts to allocate a resource from the current set of latency groups. For example, the lowest access cost is a resource within local group145A and is represented by latency group165A in the exemplary hierarchical data structure120. If, in step315, the operating system determines that it is appropriate to assign a resource from latency group165A to the thread, it makes the allocation in step320. The process300then ends. However, the allocation at this level may be unsuccessful. For example, a resource may not be available in the latency group165A or the operating system may decide against the allocation for other considerations such as spreading out resource allocation. If step315was an unsuccessful allocation, then process300continues at step325.

Step325is a check to see if the current latency group only contain the root node. If so, the process300goes to step330as the resource allocation has failed. The process300then ends. If the current latency group is not the root node, then the process300continues at step340.

In step340ofFIG. 3, the parent(s) of the current set of latency groups are made the new current set of latency groups. The process300then returns to step315. For example, the operating system attempts to allocate resources at the parent(s) of the current node (e.g.,FIG. 1A,165A). Traversing up the exemplary hierarchical data structure120orFIG. 1A, the next best alternatives are represented in the second level the exemplary hierarchical data structure120by latency group165AB, which has a latency of two units, and latency group165AC, which has a latency of four units. The operating system may choose to allocate a resource in the parent with the lowest access cost. However, a resource from the parent with the higher access may be allocated, if desired. If a suitable resource is found in the current set of latency groups, then the resource is allocated in step320. Otherwise, the process returns to step340with one of the parent latency groups becoming the current ones. For example, the current latency groups are now165AB and165AC whose parents are latency groups165ACB,165BAC, and165ABC, which have latencies of seven, six, and five units, respectively. Again, the operating system may allocate the lower access cost group; however, that is not required. The process300may repeat steps315-340until a suitable resource has been found or the process300exits with a failed allocation in step330. By traversing the exemplary hierarchical data structure120, the operating system learns the nearest resource, next nearest resources, etc.

The operating system may decide to allocate other than the nearest resource in terms of access cost. In one embodiment, the application of the hierarchical data structure is to balance the load across the local groups. For example, the operating system assigns each thread to a latency group and keeps track of how many threads are assigned to each latency group to balance the load across them. Furthermore, the operating system may optimize the bandwidth for a thread by assigning it to a non-leaf latency group such that its resources come from a wider range of local groups. For example, a thread assigned to the root latency group will spread it resources across the entire machine. In another example, a thread assigned to the latency group165AB ofFIG. 1Awill spread its resources across local groups145A and145B ofFIG. 1B.

In one embodiment of the present invention, the operating system or an application program uses the hierarchical data structure120to monitor resource allocation. For example, the hierarchical data structure120is traversed to determine what the various access costs are for the set of resources that have been allocated.

FIG. 4illustrates circuitry of computer system100, which may form a platform for embodiments of the present invention. For example, processes200and300ofFIGS. 2 and 3, respectively, may be executed within computer system100. Computer system100includes an address/data bus99for communicating information, a central processor101coupled with the bus99for processing information and instructions, a volatile memory102(e.g., random access memory RAM) coupled with the bus99for storing information and instructions for the central processor101and a non-volatile memory103(e.g., read only memory ROM) coupled with the bus99for storing static information and instructions for the processor101. Computer system100also includes an optional data storage device104(e.g., a magnetic or optical disk and disk drive) coupled with the bus99for storing information and instructions.

With reference still toFIG. 4, system100of the present invention also includes an optional alphanumeric input device106including alphanumeric and function keys is coupled to bus99for communicating information and command selections to central processor unit101. System100also optionally includes a cursor control device107coupled to bus99for communicating user input information and command selections to central processor unit101. System100of the present embodiment also includes an optional display device105coupled to bus99for displaying information. Signal input/output communication devices108coupled to bus99provides communication with external devices. The preferred embodiment of the present invention a method and system of facilitating resource allocation in a computer system, is thus described. While the present invention has been described in particular embodiments, it should be appreciated that the present invention should not be construed as limited by such embodiments, but rather construed according to the below claims.