Emerson AXP1406, AXP1600 manual Adaptive Adjustment of the Minimum Fan Level

System Behavior in Response to Sensor Events Adaptive Adjustment of the Minimum Fan Level

When at least one nonrecoverable temperature threshold has been exceeded on a FRU, the Shelf Manager powers down the FRU (sending them the SetPowerLevel(0) command) and refuses to power the FRU back up for COOLING_POLL_TIMEOUT* seconds. In that state, the Shelf Manager also immediately raises the level of all fans to the maximum level and keeps it at maximum.

A.4 Adaptive Adjustment of the Minimum Fan Level

The Shelf Manager changes the minimum fan level over time to prevent oscillations of the shelf between normal and abnormal cooling mode. When the shelf transitions from normal to abnormal cooling mode, this means that the current fan level is insufficient for effective cooling of the shelf. In that case, the Shelf Manager dynamically changes the minimum fan level to the current level + 1, so that next time in normal mode the Shelf Manager will not try to decrease the fan level so low. (In the case of multiple fans and different fan levels, the Shelf Manager chooses the maximum current fan level.) This makes the algorithm to converge to a certain fan level after several oscillations; at that level, the shelf operates in normal cooling mode and this is the minimum possible fan level at which the shelf can operate in normal cooling mode.

To accommodate for possible changes in the thermal load in the shelf in a long run, an additional enhancement is implemented. After the shelf stays in normal cooling mode at a stable fan level for a substantial period of time (specified as a configuration parameter NORMAL_STABLE_TIME*, with a default of 1 hour), the minimum fan level is decreased by one and the current fan level is allowed to drop to the new minimum. If the thermal load in the shelf has decreased, the shelf will continue to operate at the reduced fan level. Otherwise, the shelf will transition to the abnormal cooling state and the fan level will converge to a new stable value after several oscillations.

142 AXP1406/AXP1600 Subsystem IPMI Programmer’s Reference (6806800B66C)