On 20/1/21 3:41 am, Josef Bacik wrote:

On 1/11/21 4:41 AM, Anand Jain wrote:

quoted

Add round-robin read policy to route the read IO to the next device in 
the
round-robin order. The chunk allocation and thus the stripe-index follows
the order of free space available on devices. So to make the round-robin
effective it shall follow the devid order instead of the stripe-index
order.

Signed-off-by: Anand Jain <redacted>
-- 
RFC because: Provides terrible performance with the fio tests.
I am not yet sure if there is any io workload or a block layer
tuning that shall make this policy better. As of now just an
experimental patch.

Just drop this one, if we can't find a reason to use it then don't 
bother adding the code.  The other options have real world valuable 
uses, so stick with those.  Thanks,

  Yep. I will drop this patch in the next iteration.

  The low performance is attributed to the low number of read IO
  mergers in the block layer. The consecutive blocks in my test case
  (fio random read) were read from the other disk, so the block layer
  lost the opportunity to merge the IOs.

Thanks, Anand

Josef