[dm-devel] multipath multibus performance

[malahal at us.ibm.com]

Andy [genanr at emsphone.com] wrote:
> I would like to increase the performance of the multibus mode of multipath. 
> It would be nice if multibus performance would be very close to accessing
> the device directly.  From what I have been told, under multibus, I/O's are
> broken up into bio's and sent down the multiple paths, with no merging of
> adjacent I/O's.

Not quite correct. It depends on the path selector algorithm you use.
"round_robin" with rr_min_io set to 1 will definitely give you bad
performance for sequential I/O. If you set rr_min_io to a big number,
the adjacent I/Os may be merged together. What values did you use in
your testing?

--Malahal.