single cpu thread performance limit?

I seem to have hit a significant hard stop in MD RAID1/10 performance
which seems to be linked to a single CPU thread.

I am using extremely high speed (IOPS) internal block devices – 8 in
total.  They are capable of achieving > 1million iops.

However if I use RAID1 / 10 then MD seems to use a single thread which
will reach 100% CPU utilisation (single core) at around 200K IOPS.
Limiting the entire performance to around 200K.

If I use say 4 x RAID1 / 10’s and a RAID0 on top – I see not much
greater results. (although the theory seems to say I should and there
are now 4 CPU threads running, it still seems to hit 4 x 100% at maybe
350K).

Is there any way to increase the number of threads per RAID set? Or
any other suggestions on configurations?  (I have tried every
permutation of R0+R1/10’s)

Thank you for any advice.


Mark
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