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authorMarkus Stockhausen <stockhausen@collogia.de>2014-12-15 12:57:05 +1100
committerNeilBrown <neilb@suse.de>2015-04-22 08:00:42 +1000
commitd06f191f8ecaef4d524e765fdb455f96392fbd42 (patch)
tree3e83449b9fb3c910a7a6d65a776304dd158e18c4 /scripts
parent584acdd49cd2472ca0f5a06adbe979db82d0b4af (diff)
md/raid5: introduce configuration option rmw_level
Depending on the available coding we allow optimized rmw logic for write operations. To support easier testing this patch allows manual control of the rmw/rcw descision through the interface /sys/block/mdX/md/rmw_level. The configuration can handle three levels of control. rmw_level=0: Disable rmw for all RAID types. Hardware assisted P/Q calculation has no implementation path yet to factor in/out chunks of a syndrome. Enforcing this level can be benefical for slow CPUs with hardware syndrome support and fast SSDs. rmw_level=1: Estimate rmw IOs and rcw IOs. Execute rmw only if we will save IOs. This equals the "old" unpatched behaviour and will be the default. rmw_level=2: Execute rmw even if calculated IOs for rmw and rcw are equal. We might have higher CPU consumption because of calculating the parity twice but it can be benefical otherwise. E.g. RAID4 with fast dedicated parity disk/SSD. The option is implemented just to be forward-looking and will ONLY work with this patch! Signed-off-by: Markus Stockhausen <stockhausen@collogia.de> Signed-off-by: NeilBrown <neilb@suse.de>
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