On ext4 filesystems,
ext4-dio-unwrittenworkqueue should be single threaded instead of one thread per CPU.
If users isolate a realtime application to a single core (to benefit from cache coherency/cache hit), then if the
ext4-dio-unwrittenthreads also process conversions from unwritten extents to written for IOs completed from async direct IO path, the application gets a performance hit.
Per filesystem thread to write unwritten extent to written IO is enough, we don't need per cpu threads to work on conversion.
- Red Hat Enterprise Linux (RHEL) 6 up to RHEL6.4.
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