Re: [PATCH RFC - TAKE TWO - 12/12] block, bfq: boost the throughput with random I/O on NCQ-capable HDDs

[Tejun Heo]

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
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