I start to wonder (again) which scheduler is better for ceph on SSD.
My reasoning.
None:
1. Reduces latency for requests. The lower latency is, the higher is
perceived performance for unbounded workload with fixed queue depth
(hello, benchmarks).
2. Causes possible spikes in latency for requests because of the
'unfair' request ordering (hello, deep scrub).
Deadline-mq:
1. Reduce size of nr_requests (queue size) to 256 (noop shows me
916???). Make introduce latency.
2. May reduce latency spikes due to different rates for different types
of workloads.
I'm doing some benchmarks, and they, but of course, gives higher marks
for 'none' scheduler. Nevertheless, I believe most of normal workload on
Ceph does not utilize it with unbounded rate, so bounded (f.e. app
making IO based on external independed events) workload can be hurt by
lack of disk scheduler in presence of unbounded workload.
Any ideas?
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