Clock Comparator on Shared Processors

The clock comparator has the same format as bits 0-63 of the TOD clock. The clock comparator nominally consists of bits 0-47, which are compared with the corresponding bits of the TOD clock. On some models, higher resolution is obtained by providing more than 48 bits. In most cases, a logical processor running in a logical partition receives the model's resolution for the clock comparator.

However, when using shared logical processors in a logical partition, if the operating system running in a logical partition loads an enabled wait state with a clock comparator set on that logical processor, the PR/SM Hypervisor tracks that clock comparator value for the logical partition's processor at a less granular resolution. The granularity can be reduced to as little as bits 0-45 of the intended clock comparator value. This effect is not seen on dedicated logical processors nor is it seen on logical processors that are not in wait state.