Oracle® VM Server for SPARC 3.3 Administration Guide

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Updated: October 2015

CPU Allocation

When you run threads from the same core in separate domains, you might experience unpredictable and poor performance. The Oracle VM Server for SPARC software uses the CPU affinity feature to optimize CPU allocation during the logical domain binding process, which occurs before you can start the domain. This feature attempts to keep threads from the same core allocated to the same logical domain because this type of allocation improves cache sharing between the threads within the same core.

CPU affinity attempts to avoid the sharing of cores among domains unless there is no other recourse. When a domain has been allocated a partial core and requests more strands, the strands from the partial core are bound first, and then another free core is located to fulfill the request, if necessary.

    The CPU allocation mechanism uses the following constraints for CPU resources:

  • Whole-core constraint. This constraint specifies that CPU cores are allocated to a domain rather than virtual CPUs. As long as the domain does not have the max-cores constraint enabled, the whole-core constraint can be added or removed by using the ldm set-core or ldm set-vcpu command, respectively. The domain can be inactive, bound, or active. However, enough cores must be available to satisfy the request to apply the constraint. As a worst-case example, if a domain that shares cores with another domain requests the whole-core constraint, cores from the free list would need to be available to satisfy the request. As a best-case example, all the virtual CPUs in the core are already on core boundaries, so the constraint is applied without changes to CPU resources.

  • Maximum number of cores (max-cores) constraint. This constraint specifies the maximum number of cores that can be assigned to a bound or active domain.