https://bugzilla.kernel.org/show_bug.cgi?id=201685

--- Comment #229 from Jens Axboe (axboe@kernel.dk) ---

(In reply to Guenter Roeck from comment #228)

I guess I should have been more specific. With CONFIG_SCSI_MQ_DEFAULT=y (or
scsi_mod.use_blk_mq=1), cfq is not available. That applies to any kernel
version with CONFIG_SCSI_MQ_DEFAULT=y (or scsi_mod.use_blk_mq=1), not just
to 4.19, and it doesn't apply to 4.19 if CONFIG_SCSI_MQ_DEFAULT=n (or
scsi_mod.use_blk_mq=0).

It is quite irrelevant if other schedulers are available if
CONFIG_SCSI_MQ_DEFAULT=y (or scsi_mod.use_blk_mq=1). cfq is not available,
and it doesn't matter if it is set as default or not.

I hope this is specific enough this time. My apologies if I missed some
other means to enable or disable blk_mq.

My clarification was for Steven, not you.

In terms of scheduler, CFQ will change the patterns a lot. For the non-mq case,
I'd recommend using noop or deadline for testing, otherwise I fear we're
testing a lot more than mq vs non-mq.

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