On Thu, May 29, 2014 at 11:05:43AM +0200, Paolo Valente wrote:

This patch is basically the counterpart of patch 13 for NCQ-capable
rotational devices. Exactly as patch 13 does on flash-based devices
and for any workload, this patch disables device idling on rotational
devices, but only for random I/O. More precisely, idling is disabled
only for constantly-seeky queues (see patch 7). In fact, only with
these queues disabling idling boosts the throughput on NCQ-capable
rotational devices.

To not break service guarantees, idling is disabled for NCQ-enabled
rotational devices and constantly-seeky queues only when the same
symmetry conditions as in patch 13, plus an additional one, hold. The
additional condition is related to the fact that this patch disables
idling only for constantly-seeky queues. In fact, should idling be

Wouldn't it make more sense to limit queue depth to one unless the
workload can clearly benefit from allowing higher queue depth?  And I
really think it'd bring more clarity if we just concentrate on
rotational devices.

Thanks.

-- 
tejun