[PATCH v8 05/11] null_blk: allow non power of 2 zoned devices

[Chaitanya Kulkarni]

> Performance Measurement:
> 
> Device:
> zone size = 128M, blocksize=4k
> 
> FIO cmd:
> 
> fio --name=zbc --filename=/dev/nullb0 --direct=1 --zonemode=zbd  --size=23G
> --io_size=<iosize> --ioengine=io_uring --iodepth=<iod> --rw=<mode> --bs=4k
> --loops=4
> 
> The following results are an average of 4 runs on AMD Ryzen 5 5600X with
> 32GB of RAM:
> 
> Sequential Write:
> 
> x-----------------x---------------------------------x---------------------------------x
> |     IOdepth     |            8                    |            16                   |
> x-----------------x---------------------------------x---------------------------------x
> |                 |  KIOPS   |BW(MiB/s) | Lat(usec) |  KIOPS   |BW(MiB/s) | Lat(usec) |
> x-----------------x---------------------------------x---------------------------------x
> | Without patch   |  578     |  2257    |   12.80   |  576     |  2248    |   25.78   |
> x-----------------x---------------------------------x---------------------------------x
> |  With patch     |  581     |  2268    |   12.74   |  576     |  2248    |   25.85   |
> x-----------------x---------------------------------x---------------------------------x
> 
> Sequential read:
> 
> x-----------------x---------------------------------x---------------------------------x
> | IOdepth         |            8                    |            16                   |
> x-----------------x---------------------------------x---------------------------------x
> |                 |  KIOPS   |BW(MiB/s) | Lat(usec) |  KIOPS   |BW(MiB/s) | Lat(usec) |
> x-----------------x---------------------------------x---------------------------------x
> | Without patch   |  667     |  2605    |   11.79   |  675     |  2637    |   23.49   |
> x-----------------x---------------------------------x---------------------------------x
> |  With patch     |  667     |  2605    |   11.79   |  675     |  2638    |   23.48   |
> x-----------------x---------------------------------x---------------------------------x
> 
> Random read:
> 
> x-----------------x---------------------------------x---------------------------------x
> | IOdepth         |            8                    |            16                   |
> x-----------------x---------------------------------x---------------------------------x
> |                 |  KIOPS   |BW(MiB/s) | Lat(usec) |  KIOPS   |BW(MiB/s) | Lat(usec) |
> x-----------------x---------------------------------x---------------------------------x
> | Without patch   |  522     |  2038    |   15.05   |  514     |  2006    |   30.87   |
> x-----------------x---------------------------------x---------------------------------x
> |  With patch     |  522     |  2039    |   15.04   |  523     |  2042    |   30.33   |
> x-----------------x---------------------------------x---------------------------------x
> 
> Minor variations are noticed in Sequential write with io depth 8 and
> in random read with io depth 16. But overall no noticeable differences
> were noticed

minor variations in with aspect of the performance ?
are these documented somewhere ?

move the large table of performance numbers to the cover letter it looks 
ugly in the git log...