Re: can we drop the bio based path in null_blk

[Chaitanya Kulkarni <chaitanyak@nvidia.com>]

Christoph,

On 1/25/24 00:15, Christoph Hellwig wrote:
> On Wed, Jan 24, 2024 at 09:31:25PM +0100, Pankaj Raghav (Samsung) wrote:
>> The subject says removing the bio mode in null_blk but here you are
>> asking an open question about the non-so-relevant ones should move to
>> blk-mq. My input is for the latter part, FWIW.
> Well, it's two different things.  My prime concern right now is
> null_blk, which is very clumsy due to the two different I/O paths,
> and actually broken in that the bio mode doesn't respect various
> I/O limits that can be configured, and at least in zone modes also
> ones that aren't configured but required (I/Os spanning zones).
>
>

Focusing on null_blk :-

removing bio mode will significantly simplify null_blk code, but then which
bio based driver we should use as a replacement to :-

1. Establish baseline stability of block layer bio mode ? fio verify 
test etc..
2. Establish performance consistency of block layer bio mode driver across
    different kernel release?
3. Which driver one should use to compare the bio vs mq mode performance
    comparison without the need of real H/W ?

one candidate comes to mind is brd for #1 & #2, but unfortunately it doesn't
support blk-mq mode so #3 is still an open question or we don't have to 
worry
about #3 at all ?

-ck