On 4/22/21 2:20 PM, Ming Lei wrote: > Currently bio based IO polling needs to poll all hw queue blindly, this > way is very inefficient, and one big reason is that we can't pass any > bio submission result to blk_poll(). > > In IO submission context, track associated underlying bios by per-task > submission queue and store returned 'cookie' in bio->bi_poll_data which > is added by filling a hole of .bi_iter, and return current->pid to > caller of submit_bio() for any bio based driver's IO, which is > submitted from FS. > > In IO poll context, the passed cookie tells us the PID of submission > context, then we can find bios from the per-task io pull context of > submission context. Moving bios from submission queue to poll queue of > the poll context, and keep polling until these bios are ended. Remove > bio from poll queue if the bio is ended. Add bio flags of BIO_DONE and > BIO_END_BY_POLL for such purpose. > > In was found in Jeffle Xu's test that kfifo doesn't scale well for a > submission queue as queue depth is increased, so a new mechanism for > tracking bios is needed. So far bio's size is close to 2 cacheline size, > and it may not be accepted to add new field into bio for solving the > scalability issue by tracking bios via linked list, switch to bio group > list for tracking bio, the idea is to reuse .bi_end_io for linking bios > into a linked list for all sharing same .bi_end_io(call it bio group), > which is recovered before ending bio really, since BIO_END_BY_POLL is > added for enhancing this point. Usually .bi_end_bio is same for all > bios in same layer, so it is enough to provide very limited groups, such > as 16 or less for fixing the scalability issue. > > Usually submission shares context with io poll. The per-task poll context > is just like stack variable, and it is cheap to move data between the two > per-task queues. > > Also when the submission task is exiting, drain pending IOs in the context > until all are done. > > Tested-by: Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx> > Reviewed-by: Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx> > Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx> > --- > block/bio.c | 5 + > block/blk-core.c | 39 ++++- > block/blk-ioc.c | 3 + > block/blk-poll.c | 345 +++++++++++++++++++++++++++++++++++++- > block/blk.h | 33 ++++ > include/linux/blk_types.h | 27 ++- > 6 files changed, 448 insertions(+), 4 deletions(-) > Reviewed-by: Hannes Reinecke <hare@xxxxxxx> Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@xxxxxxx +49 911 74053 688 SUSE Software Solutions Germany GmbH, 90409 Nürnberg GF: F. Imendörffer, HRB 36809 (AG Nürnberg)
