How does mclock work?

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Could someone please explain how mclock works regarding reads and writes? Does mclock intervene on both read and write iops? Or only on reads or only on writes? 
And what type of underlying hardware performance is calculated and considered by mclock? Seems to be only write performance. 
The mclock documentation shows HDDs and SSDs specific configuration options (capacity and sequential bandwidth) but nothing regarding hybrid setups and these configuration options do not distinguish reads and writes. But read and write performance are often not in par for a single drive and even less when using hybrid setups. 
With hybrid setups (RocksDB+WAL on SSDs or NVMes and Data on HDD), if mclock only considers write performance, it may fail to properly schedule read iops (does mclock schedule read iops?) as the calculated iops capacity would be way too high for reads. 
With HDD only setups (RocksDB+WAL+Data on HDD), if mclock only considers write performance, the OSD may not take advantage of higher read performance. 
Can someone please shed some light on this? 
Best regards,   
Frédéric Nass 

Sous-direction Infrastructures et Services
Direction du Numérique 
Université de Lorraine
Tél : +33 3 72 74 11 35  
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