blk-mq, scsi-mq, UFS

[Andras Kovacs]

Hi all,

could someone explain to me:

- what is the difference between blk-mq and scsi-mq
- why don't I observe large speedups when running the same tiotests on Linux
v3.12 (which has no blk-mq) and Linux v3.14 (which does have blk-mq) on a
Xilinx Zynq development board (the two Linux versions are configured by
Xilinx Zynq and I know only how to add kernel command line parameters)?
- when Linux v3.17 becomes available (and Xilinx Zynq ports it for their
development board) will I see large speedups reading/writing to the target
SDD (which is driven through the UFS driver)?

Any and all info would be greatly appreciated.

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[Andras Kovacs]

Andras Kovacs <neoteny <at> freemail.hu> writes:

reading/writing to the target SDD (which is driven through the UFS driver)?

Of course I meant SSD.


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[Matias Bjorling]

Post by Andras Kovacs
Hi all,
- what is the difference between blk-mq and scsi-mq

blk-mq is the actual block layer, while scsi-mq enables the scsi
subsystem to use blk-mq. Any driver that wish to use blk-mq, has to
explicit hook into it.

Post by Andras Kovacs
- why don't I observe large speedups when running the same tiotests on Linux
v3.12 (which has no blk-mq) and Linux v3.14 (which does have blk-mq) on a
Xilinx Zynq development board (the two Linux versions are configured by
Xilinx Zynq and I know only how to add kernel command line parameters)?

Only the virtio driver (and the null blk driver) have been converted to
blk-mq in 3.14.

Post by Andras Kovacs
- when Linux v3.17 becomes available (and Xilinx Zynq ports it for their
development board) will I see large speedups reading/writing to the target
SDD (which is driven through the UFS driver)?

Depends if you're CPU bound. If you are, then a speedup is expected. You
will at least see lower CPU usage.

scsi-mq has to be explicit enabled with the scsi_mod.use_blk_mq=Y in the
kernel boot options for 3.17 until it is marked stable.

Post by Andras Kovacs
Any and all info would be greatly appreciated.
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[Andras Kovacs]

Matias Bjorling <m <at> bjorling.me> writes:

Thank you for your answers; now things are somewhat clearer.


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