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Merge pull request #54079 from zdover23/wip-doc-2023-10-19-backport-5…
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reef: doc: Update mClock QOS documentation to discard osd_mclock_cost_per_*
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anthonyeleven committed Oct 18, 2023
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Expand Up @@ -114,29 +114,6 @@ baseline throughput for each device type was determined:
256 KiB. For HDDs, it was 40MiB. The above throughput was obtained
by running 4 KiB random writes at a queue depth of 64 for 300 secs.

Factoring I/O Cost in mClock
============================

The services using mClock have a cost associated with them. The cost can be
different for each service type. The mClock scheduler factors in the cost
during calculations for parameters like *reservation*, *weight* and *limit*.
The calculations determine when the next op for the service type can be
dequeued from the operation queue. In general, the higher the cost, the longer
an op remains in the operation queue.

A cost modeling study was performed to determine the cost per I/O and the cost
per byte for SSD and HDD device types. The following cost specific options are
used under the hood by mClock,

- :confval:`osd_mclock_cost_per_io_usec`
- :confval:`osd_mclock_cost_per_io_usec_hdd`
- :confval:`osd_mclock_cost_per_io_usec_ssd`
- :confval:`osd_mclock_cost_per_byte_usec`
- :confval:`osd_mclock_cost_per_byte_usec_hdd`
- :confval:`osd_mclock_cost_per_byte_usec_ssd`

See :doc:`/rados/configuration/mclock-config-ref` for more details.

MClock Profile Allocations
==========================

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