[dm-devel] [LSF/MM ATTEND] plan to deprecate old .request_fn request-based code path?
Mikulas Patocka
mpatocka at redhat.com
Tue Jan 12 23:39:21 UTC 2016
On Tue, 12 Jan 2016, Mike Snitzer wrote:
> Hi,
>
> I'd like to attend LSF/MM and as the subject covers I'd like to at least
> participate in a discussion about plans (realistic or not) for
> removing/deprecating the old .request_fn path in block core and block
> drivers.
>
> The request-based DM code (only used for multipath) has gotten more
> complex to support both old .request_fn and blk-mq (and stacking
> combinations: .request_fn ontop of blk-mq paths, blk-mq ontop of
> .request_fn paths). Simplifying DM core in this area would be nice.
>
> One of the hurdles has been blk-mq doesn't yet have a scheduler. I know
> Jens had/has something in the works. But there is also the question of
> whether DM's top-level blk-mq request_queue should be trained to
> leverage/stack underlying blk-mq request_queue capabilities (Keith Busch
> was going to look at this aspect in the context of multipath on NVMe but
> I never heard anything from Keith on that). As of now DM multipath's
> blk-mq request_queue only supports a single (virtual) hw queue.
>
> In addition to the above topic, I'd be open to discussing Linux MD
> maintainership options with others if for some reason that is still an
> unresolved situation come mid April.
>
> Thanks,
> Mike
Convert multipath from request-based to bio-based and these problems in
device mapper core will disappear :-)
Mikulas
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